Don't complain on missing colorscheme

If we bootstrap from empty repo, vim will complain about missing
colorscheme, since we don't have it yet. Added silent before the
colorscheme command, so that we can do non-disruptive config update.

vimrc

@@ -724,7 +724,9 @@ if has('gui_running')
     "Turn off annoying beep
     au GUIEnter * set vb t_vb=
 endif
-colorscheme wombat256grf
+
+silent! colorscheme wombat256grf
+
 if $TERM == 'linux' && !has('gui_running')
     " fallback to basic 8-color colorscheme
     colorscheme pablo