Editors: minor editing changes

First and foremost, there's a change to the appropriate "its".  Yes, it doesn't follow the rule of apostrophes with possessives like everything else, but that's English for ya.

Secondly, "move around your code fast" sounds a bit awkward; "quickly move around your code" is a bit better, I think.
Merge pull request #489 from xiongchiamiov/master

Editors: minor editing changes