config: add an npm script to output current electron versions

electron-version.js

@@ -0,0 +1,2 @@
+console.log(process.versions);
+process.exit(0);

package.json

@@ -14,6 +14,7 @@
     "postinstall": "npm run rebuild",
     "start": "electron . --enable-logging --dev",
     "rebuild": "electron-rebuild -f -b -t prod,dev,optional",
+    "electron-version": "electron electron-version.js",
     "typeorm:migrate": "npm run typeorm:migrate:library",
     "typeorm:migrate:library": "typeorm migration:run -c library",
     "build:webpack": "webpack --config webpack.config.js",