json schema validation: enforce lowerCamelCase keys

There is a json schema definition for the `canoncial-data.json` file.
https://github.com/exercism/problem-specifications/blob/master/canonical-schema.json

However this still allows for arbitrary keys containing spaces.
These keys are often used for specifying test input arguments.

https://github.com/exercism/problem-specifications/blob/637cca615dbbb52d61d0a7a74d71c09360bdebf4/exercises/food-chain/canonical-data.json#L21

**Task**

Update the https://github.com/exercism/problem-specifications/blob/master/canonical-schema.json to require all keys to be lowerCamelCase