chore(package): update webpack-dev-server to version 3.1.2 (#71)

Author: greenkeeper[bot]

package.json

@@ -53,7 +53,7 @@
     "react": "^16.0.0",
     "redux": "^3.6.0",
     "webpack": "^4.0.0",
-    "webpack-dev-server": "^2.4.1"
+    "webpack-dev-server": "^3.1.2"
   },
   "jest": {
     "coverageThreshold": {