fix(package): update ajv to version 6.0.0

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "uglify-es": "^3.2.2"
   },
   "dependencies": {
-    "ajv": "^5.5.2",
+    "ajv": "^6.0.0",
     "fast-safe-stringify": "^1.2.1"
   }
 }