Replace {{tokens}} with {tokens} in docs

Looks like my editor has space problems. Really just for [this](https://github.com/mapbox/mapbox-gl-style-spec/blob/ec729dd28480013339e213958ce4b5845054d8db/docs/_generate/index.html#L269)
```
-  "text-name": "{{MY_FIELD}}"
 +  "text-name": "{MY_FIELD}"
```
related to [js pull #533](https://github.com/mapbox/mapbox-gl-js/pull/533)