extract nightwatch-helpers into npm package

Author: yyx990803

build/nightwatch.config.js

@@ -2,8 +2,8 @@
 module.exports = {
   'src_folders': ['test/e2e/specs'],
   'output_folder': 'test/e2e/reports',
-  'custom_commands_path': ['test/e2e/custom-commands'],
-  'custom_assertions_path': ['test/e2e/custom-assertions'],
+  'custom_commands_path': ['node_modules/nightwatch-helpers/commands'],
+  'custom_assertions_path': ['node_modules/nightwatch-helpers/assertions'],
 
   'selenium': {
     'start_process': true,

package.json

@@ -75,6 +75,7 @@
     "karma-webpack": "^1.7.0",
     "lodash": "^4.13.1",
     "nightwatch": "^0.9.0",
+    "nightwatch-helpers": "^1.0.0",
     "phantomjs-prebuilt": "^2.1.1",
     "rollup": "^0.33.0",
     "rollup-plugin-alias": "^1.2.0",