Prefer interpolation to concatenation

Library/Homebrew/cmd/--config.rb

@@ -69,7 +69,7 @@ module Homebrew extend self
 
   def describe_x11
     return "N/A" unless MacOS::XQuartz.installed?
-    return "#{MacOS::XQuartz.version} => " + describe_path(MacOS::XQuartz.prefix)
+    return "#{MacOS::XQuartz.version} => #{describe_path(MacOS::XQuartz.prefix)}"
   end
 
   def describe_perl