Add ajv as a dependency to stop prettier-eslint-cli from squawking

services/chat/package.json

@@ -27,6 +27,7 @@
     "v8-profiler": "^5.6.5"
   },
   "devDependencies": {
+    "ajv": "^5.5.2",
     "bunyan": "^1.0.0",
     "chai": "",
     "eslint": "^5.11.1",