fix dependencies

package.json

@@ -19,8 +19,10 @@
   "dependencies": {
     "async": "~1.2.1"
   },
-  "devDependencies": {},
+  "devDependencies": {
+    "mocha": "^2.4.5"
+  },
   "scripts": {
-  "test": "mocha"
+    "test": "mocha"
   }
 }