Prefix hashes with underscores based on CSS spec

To match with https://github.com/webpack/css-loader/blob/master/lib/getLocalIdent.js#L15

Author: longlho

index.js

@@ -41,6 +41,6 @@ module.exports = function createGenerator(pattern, options) {
     var genericName = interpolateName(loaderContext, name, loaderOptions);
     return genericName
       .replace(new RegExp('[^a-zA-Z0-9\\-_\u00A0-\uFFFF]', 'g'), '-')
-      .replace(/^([^a-zA-Z_])/, '_$1');
+      .replace(/^((-?[0-9])|--)/, "_$1");
   };
 };