Add new plugin to update script
Squashed 'bundle/vim-gitgutter/' content from commit 24efce0

git-subtree-dir: bundle/vim-gitgutter
git-subtree-split: 24efce03cc12dd30f63048627981ab911e551dd7
Merge commit 'b50d222032deab6956c873fffbf3ab282b85de50' as 'bundle/vim-gitgutter'
Configure gitgutter