Enable spell checking for git commits.

Source: http://stackoverflow.com/questions/1691060/vim-set-spell-in-file-git-commit-editmsg

vim/ftplugin/gitcommit.vim

@@ -0,0 +1,7 @@
+if exists("b:did_ftplugin")
+  finish
+endif
+
+let b:did_ftplugin = 1 " Don't load twice in one buffer
+
+setlocal spell