Add support for plugin option schema validation

package.json

@@ -26,6 +26,7 @@
   "dependencies": {
     "@types/lodash.at": "^4.6.3",
     "@types/moment-timezone": "^0.5.6",
+    "ajv": "^6.7.0",
     "cross-env": "^5.2.0",
     "dotenv": "^4.0.0",
     "emoji-regex": "^7.0.1",
@@ -33,7 +34,7 @@
     "escape-string-regexp": "^1.0.5",
     "humanize-duration": "^3.15.0",
     "js-yaml": "^3.12.0",
-    "knub": "^16.1.1",
+    "knub": "^16.3.0",
     "lodash.at": "^4.6.0",
     "lodash.chunk": "^4.2.0",
     "lodash.difference": "^4.5.0",