turn off webpack progress for less noisy builds

This patchset also enables linting of webpack development to ensure es6
compatability. Before this patchset, gulp was invoked with an ampersand
to make it a background process. However since it only takes a few
seconds to run, it's success messages would be interlaced with webpack's
output. This reads rather odd in our logs. Since gulp is a low-churn
tool in canvas, let's mute stdout but still display stderr if an error
should appear.

Change-Id: I48846758e839480c9bc5779bfe64201e90713e2b
Reviewed-on: https://gerrit.instructure.com/170833
Tested-by: Jenkins
Reviewed-by: Rex Fleischer <[email protected]>
QA-Review: Derek Bender <[email protected]>
Product-Review: Derek Bender <[email protected]>

package.json

@@ -228,8 +228,8 @@
     "build:packages": "yarn workspace-run build:canvas",
     "lint:browser-code": "es-check es5 ./public/dist/**/*.js",
     "postinstall": "yarn build:packages",
-    "webpack": "gulp rev & webpack --progress --color --watch",
-    "webpack-development": "gulp rev & webpack --progress --color",
+    "webpack": "gulp rev 1> /dev/null & webpack --progress --color --watch",
+    "webpack-development": "gulp rev 1> /dev/null & webpack --color && yarn lint:browser-code",
     "webpack-production": "NODE_ENV=production gulp rev && node --max_old_space_size=4096 $(yarn bin)/webpack --color --config webpack.production.config.js && yarn lint:browser-code",
     "workspace-run": "r() { wsrun $@ --fast-exit --exclude-missing --collect-logs --report; exit $?; } && r",
     "jspec": "./spec/jspec.sh",