Dropping peer dependency of mapbox-gl-js

[SnailBones]

Closes https://github.com/mapbox/mapbox-gl-rtl-text/issues/27

From https://github.com/mapbox/mapbox-gl-rtl-text/pull/28:

My suggestion is to simply drop the peerDependencies field which has a lot of annoying caveats with little benefit. We do not maintain/support ancient versions before v0.32.1, and we also do not intend to break plugin compatibility in v3.0.0 (if we ever do so, we may revisit later).