Disallow additional properties on category schema

The intent of this change is to update the schema without any test
failures. This means that other changes that affect the data should
happen independently from the pull request associated with this commit,
and it should be kept up to date and merged once the schema tests pass.
To contribute to this change, open PRs that would correct any data that
does not conform to the JSON schema. Discussion regarding other schema
updates should happen in the associated issue at #1171.

Resolves #1171.

.schemas/category.json

@@ -18,6 +18,7 @@
   "required":[
     "title"
   ],
+  "additionalProperties": false,
   "title":"Video",
   "type":"object"
 }