build: transpile the debug dependency with Babel

socketio/engine.io@a967626 has broken
the build for IE and android 5.1

Related: debug-js/debug#668

Author: darrachequesne

support/webpack.config.js

@@ -12,7 +12,7 @@ module.exports = {
   module: {
     loaders: [{
       test: /\.js$/,
-      exclude: /(node_modules|bower_components)/,
+      include: /debug/,
       loader: 'babel', // 'babel-loader' is also a legal name to reference
       query: {
         presets: ['es2015']