test: tweak test:lint command + add test:lint:fix (#15)

Author: bnb

package.json

@@ -17,7 +17,8 @@
   },
   "scripts": {
     "test": "npm run test:lint && npm run test:unit",
-    "test:lint": "standard --fix",
+    "test:lint": "standard",
+    "test:lint:fix": "standard --fix",
     "test:unit": "node test/parallel/* && node test/message && node test/node-core-test.js"
   },
   "devDependencies": {