fix selenium-server-standalone-jar package version

package.json

@@ -123,7 +123,7 @@
     "react-test-renderer": "^15.5.4",
     "rimraf": "^2.6.0",
     "sass-loader": "^6.0.2",
-    "selenium-server-standalone-jar": "^3.4.0",
+    "selenium-server-standalone-jar": "3.4.0",
     "standard": "^8.6.0",
     "standard-loader": "^5.0.0",
     "style-loader": "0.13.0",