Use default styling on button for status-bar

[vprigent]

Since Atom 1.31, the Github package has been using, for accessibility purpose, a button for the file count on the status-bar.

Before : on hover

After : on hover

Two notes here :

• This happens because we are using !important on buttons, the quick solution being to reapply important again to override the default button styling.
• I decided to override this on status-bar directly to avoid the case where Atom or the Github package were to migrate every current links as buttons