Prefix error with exclamation point

Install/Templates/home/config/fish/functions/fish_prompt.fish

@@ -26,8 +26,9 @@ function fish_prompt --description 'Write out the prompt'
     # Error status
     if not test $last_status -eq 0
         set_color $fish_color_error
-    echo -n $last_status
-    set_color normal
+	echo -n '!'
+        echo -n $last_status
+        set_color normal
     end
 
     # Purpose