simplify electron startpoint

editor/package.json

@@ -1,5 +0,0 @@
-{
-  "name"    : "your-app",
-  "version" : "0.1.0",
-  "main"    : "main.js"
-}

package.json

@@ -34,7 +34,7 @@
     "dev": "rollup -c -w",
     "lint": "eslint src",
     "test": "rollup -c test/rollup.unit.config.js -w",
-    "editor-start": "electron ./editor/"
+    "editor-start": "electron ./editor/main.js"
   },
   "keywords": [
     "three",