Make webpack exit non-zero on error

Pass `--bail` to webpack, so that if we can't find a module, we bail out rather
than deploy a broken version to /develop.

webpack/webpack#708 is somewhat relevant.

Author: richvdh

package.json

@@ -31,8 +31,8 @@
     "build:res": "node scripts/copy-res.js",
     "build:modernizr": "modernizr -c .modernizr.json -d src/vector/modernizr.js",
     "build:compile": "npm run reskindex && babel --source-maps -d lib src",
-    "build:bundle": "cross-env NODE_ENV=production webpack -p --progress",
-    "build:bundle:dev": "webpack --optimize-occurence-order --progress",
+    "build:bundle": "cross-env NODE_ENV=production webpack -p --progress --bail",
+    "build:bundle:dev": "webpack --optimize-occurence-order --progress --bail",
     "build:electron": "npm run clean && npm run build && npm run install:electron && build -wml --ia32 --x64",
     "build": "npm run reskindex && npm run build:res && npm run build:bundle",
     "build:dev": "npm run reskindex && npm run build:res && npm run build:bundle:dev",