Update to the latest Electron version (1.8.7)

It inculdes security fixes, bug fixes and improvementts. See:
https://electronjs.org/releases

Reason for upgrading from 1.7.X to 1.8.X:

"We can not reasonably back port every bug fix and every feature to
older versions of Electron. 1.8.x is now a stable release line and if
you require this fix you should update to that stream."

https://github.com/electron/electron/issues/9860#issuecomment-365517773

package.json

@@ -17,7 +17,7 @@
     "dev-start": "concurrently --kill-others \"npm run webpack\" \"npm run hot\""
   },
   "config": {
-    "electron-version": "1.7.11"
+    "electron-version": "1.8.7"
   },
   "repository": {
     "type": "git",
@@ -118,7 +118,7 @@
     "css-loader": "^0.19.0",
     "devtron": "^1.1.0",
     "dom-storage": "^2.0.2",
-    "electron": "1.7.11",
+    "electron": "1.8.7",
     "electron-packager": "^6.0.0",
     "eslint": "^3.13.1",
     "eslint-config-standard": "^6.2.1",