Simplify various git config color.* settings to color.ui

Author: tjgrathwell

sites/en/installfest/configure_git.step

@@ -16,9 +16,7 @@ end
 
 tip "Colored output in Git" do
   console <<-BASH
-git config --global color.diff auto
-git config --global color.status auto
-git config --global color.branch auto
+git config --global color.ui auto
   BASH
 
   important do