Add vim Keyword syntax coloring

Orange might not be the best choice, so I'm open to other suggestions,
but I think something is better than nothing.

Fix chriskempson/tomorrow-theme#230.
Use same color as specified at README.md

Colors of Tomorrow Night Eighties were adjusted on
chriskempson/tomorrow-theme@80185bf763dcc040d225b3dc77d02d7f99ba57ec.

Fix chriskempson/tomorrow-theme#194.
Fix chriskempson/tomorrow-theme#252.
Fix chriskempson/tomorrow-theme#255.
Merge pull request #1 from yous/vim-keyword-coloring

Add vim Keyword syntax coloring
Merge pull request #2 from yous/patch-color

Use same color as specified at README.md