ci: add firefox to ci run

Author: posva

Diff for: package.json

@@ -32,7 +32,7 @@
     "test": "npm run lint && npm run flow && npm run test:unit && npm run test:e2e && npm run test:types",
     "flow": "flow check",
     "test:unit": "jasmine JASMINE_CONFIG_PATH=test/unit/jasmine.json",
-    "test:e2e": "node test/e2e/runner.js",
+    "test:e2e": "node test/e2e/runner.js -e firefox,chrome -c test/e2e/nightwatch.config.js",
     "test:types": "tsc -p types/test",
     "docs": "vuepress dev docs",
     "docs:build": "vuepress build docs",