Upgrade electron to v4

package.json

@@ -17,7 +17,7 @@
     "watch": "webpack-dev-server --hot"
   },
   "config": {
-    "electron-version": "3.0.8"
+    "electron-version": "4.2.12"
   },
   "repository": {
     "type": "git",
@@ -147,7 +147,7 @@
     "css-loader": "^0.19.0",
     "devtron": "^1.1.0",
     "dom-storage": "^2.0.2",
-    "electron": "3.0.8",
+    "electron": "4",
     "electron-debug": "^2.2.0",
     "electron-devtools-installer": "^2.2.4",
     "electron-packager": "^12.2.0",