Fix and update CI analyzers

Make explicit "mkcert -help" print to stdout (FiloSottile#265)

Currently "mkcert -help" prints to stderr, which is rather annoying as:

	$ mkcert -help | less

Gives us a blank page, as it pipes only stdout. To get any results in
less I need to use:

	$ mkcert 2>&1 | less
	$ mkcert |& less     # Non-standard bash/ zsh

Since the user explicitly asked for help with -help, it doesn't make
much sense to output it to stderr IMHO.

Add link to Chocolatey in README (FiloSottile#181)

Add support for certificate signing requests with -csr

Closes FiloSottile#55

Refactor output path flags

nss: use certutil from $PATH if found on macOS (FiloSottile#71)

Fixes FiloSottile#70

Thanks to @hostep for testing and fixing the patch.

linux: use unique per-CA names when installing certificates

Fixes FiloSottile#52
Closes FiloSottile#59

Force go stable to workaround travis-ci/gimme#157

Add note about iOS bug to README