Update github.com/cloudflare/cfssl (letsencrypt#3528)

```
 roland@catbus  ~/code/go/src/github.com/cloudflare/cfssl   master  ./test.sh
BUILDING.md		Gopkg.toml		certdb			crl			helpers			revoke			test.sh
CHANGELOG		LICENSE			certinfo		crypto			info			scan			testdata
Dockerfile		README.md		cli			csr			initca			script			transport
Dockerfile.build	api			cmd			doc			log			selfsign		ubiquity
Dockerfile.minimal	auth			config			errors			multiroot		signer			vendor
Gopkg.lock		bundler			coverprofile.txt	gopath			ocsp			test.prof		whitelist
ok  	github.com/cloudflare/cfssl/api	1.043s	coverage: 81.1% of statements
ok  	github.com/cloudflare/cfssl/api/bundle	1.570s	coverage: 87.2% of statements
ok  	github.com/cloudflare/cfssl/api/certadd	12.607s	coverage: 86.8% of statements
ok  	github.com/cloudflare/cfssl/api/client	1.070s	coverage: 52.2% of statements
ok  	github.com/cloudflare/cfssl/api/crl	1.107s	coverage: 75.0% of statements
ok  	github.com/cloudflare/cfssl/api/gencrl	1.057s	coverage: 72.5% of statements
ok  	github.com/cloudflare/cfssl/api/generator	1.262s	coverage: 33.3% of statements
ok  	github.com/cloudflare/cfssl/api/info	1.102s	coverage: 84.1% of statements
ok  	github.com/cloudflare/cfssl/api/initca	1.073s	coverage: 90.5% of statements
ok  	github.com/cloudflare/cfssl/api/ocsp	1.116s	coverage: 93.8% of statements
ok  	github.com/cloudflare/cfssl/api/revoke	2.923s	coverage: 75.0% of statements
ok  	github.com/cloudflare/cfssl/api/scan	17.178s	coverage: 62.1% of statements
ok  	github.com/cloudflare/cfssl/api/sign	2.221s	coverage: 83.3% of statements
ok  	github.com/cloudflare/cfssl/api/signhandler	1.145s	coverage: 26.3% of statements
ok  	github.com/cloudflare/cfssl/auth	1.022s	coverage: 68.2% of statements
ok  	github.com/cloudflare/cfssl/bundler	14.899s	coverage: 84.5% of statements
ok  	github.com/cloudflare/cfssl/certdb/dbconf	1.040s	coverage: 84.2% of statements
ok  	github.com/cloudflare/cfssl/certdb/ocspstapling	1.283s	coverage: 69.2% of statements
ok  	github.com/cloudflare/cfssl/certdb/sql	1.092s	coverage: 70.5% of statements
ok  	github.com/cloudflare/cfssl/cli	1.036s	coverage: 61.9% of statements
ok  	github.com/cloudflare/cfssl/cli/bundle	1.034s	coverage: 0.0% of statements [no tests to run]
ok  	github.com/cloudflare/cfssl/cli/crl	1.106s	coverage: 57.8% of statements
ok  	github.com/cloudflare/cfssl/cli/gencert	6.106s	coverage: 83.6% of statements
ok  	github.com/cloudflare/cfssl/cli/gencrl	1.081s	coverage: 73.3% of statements
ok  	github.com/cloudflare/cfssl/cli/gencsr	1.075s	coverage: 70.3% of statements
ok  	github.com/cloudflare/cfssl/cli/genkey	2.903s	coverage: 70.0% of statements
ok  	github.com/cloudflare/cfssl/cli/ocsprefresh	1.074s	coverage: 64.3% of statements
ok  	github.com/cloudflare/cfssl/cli/revoke	1.054s	coverage: 88.2% of statements
ok  	github.com/cloudflare/cfssl/cli/scan	1.032s	coverage: 36.0% of statements
ok  	github.com/cloudflare/cfssl/cli/selfsign	2.429s	coverage: 73.2% of statements
ok  	github.com/cloudflare/cfssl/cli/serve	1.172s	coverage: 39.0% of statements
ok  	github.com/cloudflare/cfssl/cli/sign	1.058s	coverage: 54.8% of statements
ok  	github.com/cloudflare/cfssl/cli/version	1.028s	coverage: 100.0% of statements
ok  	github.com/cloudflare/cfssl/cmd/cfssl	1.196s	coverage: 0.0% of statements [no tests to run]
ok  	github.com/cloudflare/cfssl/cmd/cfssljson	1.031s	coverage: 3.4% of statements
ok  	github.com/cloudflare/cfssl/cmd/mkbundle	1.032s	coverage: 0.0% of statements [no tests to run]
ok  	github.com/cloudflare/cfssl/config	1.054s	coverage: 67.7% of statements
ok  	github.com/cloudflare/cfssl/crl	1.072s	coverage: 68.3% of statements
ok  	github.com/cloudflare/cfssl/csr	20.657s	coverage: 89.6% of statements
ok  	github.com/cloudflare/cfssl/errors	1.029s	coverage: 79.6% of statements
ok  	github.com/cloudflare/cfssl/helpers	1.225s	coverage: 82.8% of statements
ok  	github.com/cloudflare/cfssl/helpers/testsuite	6.558s	coverage: 65.8% of statements
ok  	github.com/cloudflare/cfssl/initca	81.870s	coverage: 73.2% of statements
ok  	github.com/cloudflare/cfssl/log	1.019s	coverage: 59.3% of statements
ok  	github.com/cloudflare/cfssl/multiroot/config	1.190s	coverage: 77.4% of statements
ok  	github.com/cloudflare/cfssl/ocsp	1.226s	coverage: 77.4% of statements
ok  	github.com/cloudflare/cfssl/revoke	1.832s	coverage: 77.9% of statements
ok  	github.com/cloudflare/cfssl/scan	1.042s	coverage: 1.1% of statements
ok  	github.com/cloudflare/cfssl/selfsign	1.073s	coverage: 70.0% of statements
ok  	github.com/cloudflare/cfssl/signer	1.030s	coverage: 19.4% of statements
ok  	github.com/cloudflare/cfssl/signer/local	3.171s	coverage: 78.1% of statements
ok  	github.com/cloudflare/cfssl/signer/remote	2.197s	coverage: 70.0% of statements
ok  	github.com/cloudflare/cfssl/signer/universal	2.061s	coverage: 67.7% of statements
ok  	github.com/cloudflare/cfssl/transport	1.031s
ok  	github.com/cloudflare/cfssl/transport/ca/localca	1.062s	coverage: 94.9% of statements
ok  	github.com/cloudflare/cfssl/transport/core	1.054s	coverage: 90.9% of statements
ok  	github.com/cloudflare/cfssl/transport/kp	1.059s	coverage: 37.1% of statements
ok  	github.com/cloudflare/cfssl/transport/roots/system	1.384s	coverage: 77.1% of statements
ok  	github.com/cloudflare/cfssl/ubiquity	1.057s	coverage: 88.3% of statements
ok  	github.com/cloudflare/cfssl/whitelist	2.060s	coverage: 100.0% of statements
```