Use BASH to get Ruby version, not AWK

No need for AWK there. By using just `read` (builtin), instead of
AWK, this commit winds up being a considerable optimization.

NOTE: The `_` is just commonly used to indicate junk; not used.

themes/base.theme.bash

@@ -420,7 +420,7 @@ function chruby_version_prompt {
 			chruby_auto
 		fi
 
-		ruby_version=$(ruby --version | awk '{print $1, $2;}') || return
+		read _ ruby_version _ <<< "$(ruby --version)" || return
 
 		if ! chruby | grep -q '\*'; then
 			ruby_version="${ruby_version} (system)"