Upgrade dependencies (#996)

* Upgrade Electron to 5.0.4

* Fix spellcheck provider

* npm audit fix

package.json

@@ -51,8 +51,8 @@
     "cross-env": "^5.2.0",
     "css-loader": "^1.0.1",
     "devtron": "^1.4.0",
-    "electron": "^4.2.4",
-    "electron-builder": "20.38.2",
+    "electron": "^5.0.4",
+    "electron-builder": "^20.44.4",
     "electron-connect": "^0.6.3",
     "eslint": "^5.9.0",
     "eslint-config-mattermost": "github:mattermost/eslint-config-mattermost",
@@ -67,7 +67,7 @@
     "npm-run-all": "^4.1.5",
     "react": "^16.6.3",
     "react-dom": "^16.6.3",
-    "spectron": "^5.0.0",
+    "spectron": "^6.0.0",
     "style-loader": "^0.23.1",
     "url-loader": "^1.1.2",
     "webpack": "^4.27.0",