Update spectron to the latest version 🚀 (#65)

* fix(package): update spectron to version 4.0.0

* chore(package): update lockfile

https://npm.im/greenkeeper-lockfile

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "lodash.merge": "^4.6.1",
     "portfinder": "^1.0.16",
     "pumpify": "^1.5.1",
-    "spectron": "^3.8.0",
+    "spectron": "^4.0.0",
     "split2": "^3.0.0",
     "through2-filter": "^3.0.0",
     "through2-map": "^3.0.0",