vim-gitgutter highlighting

Background color of sign column in gitgutter is distracting. Per
airblade's docs adding this command cleans it up
Merge pull request #313 from jacobwalker0814/vim-gitgutter

vim-gitgutter highlighting
Merge remote-tracking branch 'upstream/3.0' into 3.0
Adding Haml support
Merge remote-tracking branch 'upstream/3.0' into 3.0