Update babel flags

Author: mjackson

package.json

@@ -11,7 +11,7 @@
   "bugs": "https://github.com/rackt/react-router/issues",
   "scripts": {
     "build": "scripts/build.sh",
-    "watch": "babel ./modules --watch -d build",
+    "watch": "babel ./modules --watch -d build --optional es7.classProperties",
     "build-website": "babel-node website/scripts/build.js > website/index.html",
     "examples": "webpack-dev-server --config examples/webpack.config.js --content-base examples",
     "prepublish": "npm run build",

scripts/build.sh

@@ -6,7 +6,7 @@ build_dir=lib
 
 rm -rf $build_dir
 
-$babel -d $build_dir ./modules
+$babel ./modules -d $build_dir --optional es7.classProperties
 find -X $build_dir -type d -name __tests__ | xargs rm -rf
 NODE_ENV=production $webpack modules/index.js $build_dir/umd/ReactRouter.js
 NODE_ENV=production COMPRESS=1 $webpack modules/index.js $build_dir/umd/ReactRouter.min.js