chore(package): update superagent to version 5.1.3

Closes #103

Author: greenkeeper[bot]

package.json

@@ -192,7 +192,7 @@
     "restify": "^4.3.0",
     "restler": "3.4.0",
     "rimraf": "^2.3.2",
-    "superagent": "^3.3.1",
+    "superagent": "^5.1.3",
     "tap": "^10.3.2",
     "zombie": "^4.2.1"
   },