revert to selenium server 2.53.1 because CircleCI does not support 3 yet

build/nightwatch.config.js

@@ -7,7 +7,7 @@ module.exports = {
 
   'selenium': {
     'start_process': true,
-    'server_path': 'node_modules/selenium-server/lib/runner/selenium-server-standalone-3.0.1.jar',
+    'server_path': 'node_modules/selenium-server/lib/runner/selenium-server-standalone-2.53.1.jar',
     'host': '127.0.0.1',
     'port': 4444,
     'cli_args': {

package.json

@@ -101,7 +101,7 @@
     "rollup-plugin-flow-no-whitespace": "^1.0.0",
     "rollup-plugin-replace": "^1.1.0",
     "rollup-watch": "^2.5.0",
-    "selenium-server": "3.0.1",
+    "selenium-server": "2.53.1",
     "typescript": "^2.0.9",
     "uglify-js": "^2.6.2",
     "webpack": "^1.13.2",