chore(package): upgrade superagent (#429)

Author: leeyeh

package.json

@@ -24,7 +24,7 @@
     "localstorage-memory": "^1.0.1",
     "md5": "^2.0.0",
     "qiniu": "^6.1.11",
-    "superagent": "^2.0.0",
+    "superagent": "^3.3.1",
     "underscore": "^1.8.3"
   },
   "devDependencies": {