Fix production build (#408)

Per shakacode/react_on_rails#895

Author: justin808

client/package.json

@@ -29,8 +29,8 @@
     "test": "NODE_PATH=./app mocha --compilers js:babel-core/register --require ./app/libs/testHelper.js --require ./app/libs/testNullCompiler.js 'app/**/*.spec.@(js|jsx)'",
     "test:debug": "yarn run test -- --debug-brk",
     "start": "babel-node server-express.js",
-    "build:production:client": "NODE_ENV=production webpack --config webpack.client.rails.build.config.js",
-    "build:production:server": "NODE_ENV=production webpack --config webpack.server.rails.build.config.js",
+    "build:production:client": "NODE_ENV=production webpack -p --config webpack.client.rails.build.config.js",
+    "build:production:server": "NODE_ENV=production webpack -p --config webpack.server.rails.build.config.js",
     "build:client": "webpack --config webpack.client.rails.build.config.js",
     "build:dev:client": "NODE_ENV=development webpack -w --config webpack.client.rails.build.config.js",
     "build:dev:server": "NODE_ENV=development webpack -w --config webpack.server.rails.build.config.js",