Bump ajv from 6.10.2 to 6.12.3 (#8)

Bumps [ajv](https://github.com/ajv-validator/ajv) from 6.10.2 to 6.12.3.
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v6.10.2...v6.12.3)

---
updated-dependencies:
- dependency-name: ajv
  dependency-type: direct:development
...

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package.json

@@ -13,7 +13,7 @@
     "applicationId": "amzn1.echo-sdk-ams.app.999999-d0ed-9999-ad00-999999d00ebe"
   },
   "devDependencies": {
-    "ajv": "^6.10.2",
+    "ajv": "^6.12.3",
     "aws-sdk": "^2.553.0",
     "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",