Fix the class inheritance bug for IE <= 10

This is caused by babel bug https://github.com/babel/babel/issues/3041.
Upgrade to the latest BabelJS to fix the issue.

Also replace source map with inline source map to ease the debugging.

package.json

@@ -21,10 +21,10 @@
     "url": "https://github.com/Microsoft/backbone-toolbar.git"
   },
   "devDependencies": {
-    "babel-core": "^6.13.2",
+    "babel-core": "^6.18.0",
     "babel-loader": "^6.2.5",
-    "babel-preset-es2015": "^6.13.2",
+    "babel-preset-es2015": "^6.18.0",
-    "babel-preset-stage-3": "^6.11.0",
+    "babel-preset-stage-3": "^6.17.0",
     "backbone": "^1.3.3",
     "bootstrap": "^3.3.7",
     "bootstrap-webpack": "0.0.5",

webpack.config.js

@@ -50,5 +50,5 @@ module.exports = {
   babel: { presets: ['es2015', 'stage-3'] },
   externals: [getExternals()],
   resolve: { alias: webpackAlias },
-  devtool: 'source-map',
+  devtool: 'inline-source-map',
 };