Deprecated selector in `open-plus\styles\open-plus.less`

[shinjiNAKASHIMA]

In open-plus\styles\open-plus.less:

Starting from Atom v1.13.0, the contents of atom-text-editor elements are no longer encapsulated within a shadow DOM boundary. This means you should stop using :host and ::shadow pseudo-selectors, and prepend all your syntax selectors with syntax--. To prevent breakage with existing style sheets, Atom will automatically upgrade the following selectors:

• atom-text-editor .open-plus .region, atom-text-editor::shadow .open-plus .region => atom-text-editor .open-plus .region, atom-text-editor.editor .open-plus .region

Automatic translation of selectors will be removed in a few release cycles to minimize startup time. Please, make sure to upgrade the above selectors as soon as possible.

[amayer5125]

I have a pull request for this already #30