Use safer sign for removed line

dotfiles/vim/vimrc

 
 let g:gitgutter_sign_added = '✚'
 let g:gitgutter_sign_modified = '❱'
-let g:gitgutter_sign_removed = '❌'
+let g:gitgutter_sign_removed = 'x'
 let g:gitgutter_sign_removed_first_line = '^'
 let g:gitgutter_sign_modified_removed = '❰'