Downgrade css-loader to ^0.18.0

As per suggestion in webpack-contrib/css-loader#145

Change-Id: I45abfa4236f169277156cb4b453106c10e5bf407

Author: jhawthorn

chop/package.json

@@ -8,7 +8,7 @@
     "babel-loader": "^5.3.2",
     "babel-runtime": "^5.8.25",
     "bourbon": "^4.2.5",
-    "css-loader": "^0.19.0",
+    "css-loader": "^0.18.0",
     "extract-text-webpack-plugin": "^0.8.2",
     "node-sass": "^3.3.3",
     "nuclear-js": "^1.1.1",