Bump ajv from 6.6.2 to 6.12.3

Bumps [ajv](https://github.com/ajv-validator/ajv) from 6.6.2 to 6.12.3.
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v6.6.2...v6.12.3)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package-lock.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "dependencies": {
-    "ajv": "^6.0.0",
+    "ajv": "^6.12.3",
     "es6-promise": "^4.2.5",
     "isomorphic-fetch": "^2.2.1",
     "jquery": "^3.3.1",