Don't show useless '[]' when chruby_prompt_info is empty

themes/gallois.zsh-theme

@@ -18,7 +18,7 @@ else
   if which rbenv &> /dev/null; then
     RPS1='$(git_custom_status)%{$fg[red]%}[`rbenv version | sed -e "s/ (set.*$//"`]%{$reset_color%} $EPS1'
   else
-    if which chruby_prompt_info &> /dev/null; then
+    if [[ -n `which chruby_prompt_info` && -n `chruby_prompt_info` ]]; then
       RPS1='$(git_custom_status)%{$fg[red]%}[`chruby_prompt_info`]%{$reset_color%} $EPS1'
     else
       RPS1='$(git_custom_status) $EPS1'