Fix CSS caching issue

When the only changes are HTML or CSS the hash was not updated.
This commit should fix the issue.

For why hash is used instead of contenthash, see webpack-contrib/extract-text-webpack-plugin#763 (comment).

buildtools/webpack.commons.js

@@ -184,7 +184,7 @@ const config = function(hardSourceConfig, babelLoaderCacheDirectory) {
       providePlugin,
       new ExtractTextPlugin({
           ignoreOrder: true,
-          filename: devMode ? '[name].css' : '[name].[chunkhash:6].css'
+          filename: devMode ? '[name].css' : '[name].[hash:6].css'
       }),
       new webpack.IgnorePlugin(/^\.\/locale$/, /node_modules\/moment\/src\/lib\/locale$/),
       new HardSourceWebpackPlugin(hardSourceConfig || {}),