fix(linter.view): fix double execution at file open

The event `contents-modified` get's triggered when a new file is open,
this was causing a double execution of `@lint`.
fix(linter.view): fix double execution of `@lint` on save + on modify

I use the throttled version of `@lint` in the two cases now
Merge pull request #79 from AtomLinter/fix-double-message-statusbar

Fix double message statusbar