Deprecation of the <grammar-selector-status> element

[as-cii]

The Atom team is in the process of deprecating the usage of custom elements in core. This is a breaking change and we have noticed this package may be affected by it (atom/grammar-selector#35). To prevent breakage, we recommend using the grammar status element via its class name (.grammar-status) instead of via the element name.

Thanks! 🙇

cc: @sscotth