Bump ajv from 6.10.2 to 6.12.3

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
...

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

package.json

@@ -17,7 +17,7 @@
   },
   "homepage": "https://github.com/matthewturner/smartheat-core#readme",
   "devDependencies": {
-    "ajv": "^6.10.2",
+    "ajv": "^6.12.3",
     "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",
     "eslint": "^5.16.0",