downgrade selenium-server so that it works on CI

package.json

@@ -107,7 +107,7 @@
     "rollup-plugin-flow-no-whitespace": "^1.0.0",
     "rollup-plugin-replace": "^1.1.0",
     "rollup-watch": "^3.2.2",
-    "selenium-server": "3.0.1",
+    "selenium-server": "^2.53.1",
     "typescript": "^2.0.9",
     "uglify-js": "^2.6.2",
     "webpack": "^1.13.2",

yarn.lock

@@ -4089,9 +4089,9 @@ saucelabs@^1.3.0:
   dependencies:
     https-proxy-agent "^1.0.0"
 
-selenium-server@3.0.1:
-  version "3.0.1"
-  resolved "https://registry.yarnpkg.com/selenium-server/-/selenium-server-3.0.1.tgz#78c662d7fbdd9abbc882428a92f78e7f9f5b85bf"
+selenium-server@^2.53.1:
+  version "2.53.1"
+  resolved "https://registry.yarnpkg.com/selenium-server/-/selenium-server-2.53.1.tgz#d681528812f3c2e0531a6b7e613e23bb02cce8a6"
 
 "semver@2 || 3 || 4 || 5", semver@^5.3.0, semver@~5.3.0:
   version "5.3.0"