Use proper method to subscribe to onDidTokenize
Use proper method to subscribe to onDidTokenize

Way back in
https://github.com/atom/atom/commit/117a3fb1b57465e3164c378219eefcca4b5c22a5
(released in Atom v1.9.0-beta0) Atom introduced an experimental
TextEditor::onDidTokenize method in order to subscribe to that event.
Switch to using this instead of grabbing it through the private
properties which no longer work as of Atom v1.25.0-beta0.

Fixes #649.

atom-minimap/minimap