Add test-browser-headless script using Electron

package.json

@@ -76,6 +76,7 @@
     "brfs": "^1.2.0",
     "browserify": "^13.0.0",
     "cross-spawn-async": "^2.0.0",
+    "electron-prebuilt": "^0.36.7",
     "finalhandler": "^0.4.0",
     "run-series": "^1.0.2",
     "serve-static": "^1.9.3",
@@ -115,6 +116,7 @@
     "test": "standard && node ./bin/test.js",
     "test-browser": "zuul -- test/*.js test/browser/*.js",
     "test-browser-local": "zuul --local -- test/*.js test/browser/*.js",
+    "test-browser-headless": "zuul --electron -- test/*.js test/browser/*.js",
     "test-node": "tape test/*.js test/node/*.js"
   }
 }