chore(npm): define npm test

Author: azu

package.json

@@ -29,7 +29,7 @@
     "build": "babel src --out-dir lib --source-maps",
     "watch": "babel src --out-dir lib --watch --source-maps",
     "prepublish": "npm run --if-present build",
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "mocha"
   },
   "devDependencies": {
     "babel": "^5.8.23",