chore(package): update koa to version 1.2.2

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -26,7 +26,7 @@
   "devDependencies": {
     "eslint": "^3.3.0",
     "istanbul": "^0.4.3",
-    "koa": "^1.0.0",
+    "koa": "^1.2.2",
     "mocha": "^3.0.2",
     "supertest": "^2.0.0"
   },