chore(package): update ajv to version 5.1.1

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -28,7 +28,7 @@
   },
   "homepage": "https://github.com/JSONScript/jsonscript-proxy#readme",
   "dependencies": {
-    "ajv": "^4.1.2",
+    "ajv": "^5.1.1",
     "ajv-keywords": "^1.1.1",
     "body-parser": "^1.15.1",
     "express": "^4.13.4",