Update Electron to 0.37.8

Make sure the userData directory is created during the ready event of app
module.

Close #130

package.json

@@ -36,7 +36,7 @@
     "electron-builder": "^3.11.0",
     "electron-connect": "^0.3.7",
     "electron-packager": "^7.0.1",
-    "electron-prebuilt": "0.37.7",
+    "electron-prebuilt": "0.37.8",
     "esformatter": "^0.9.3",
     "esformatter-jsx": "^5.0.0",
     "gulp": "^3.9.0",