Deprecation warning for DocumentManager.currentDocumentChange

[petetnt]

Hi,

as of (at least) Brackets 1.1. the DocumentManager.currentDocumentChange has been deprecated in favor of MainViewManager.currentFileChange which is why Brackets throws Registering for deprecated event 'currentDocumentChange'. Instead, use MainViewManager.currentFileChange.
for this block.

I've got a PR ready that fixes this (small) issue by just switching the event if that's all right.