Fix typo in XQuartz comment

Library/Homebrew/macos/xquartz.rb

@@ -40,7 +40,7 @@ module MacOS::XQuartz extend self
   end
 
   # This should really be private, but for compatibility reasons it must
-  # remain public. New code should use MacOS::XQuartz.{bin,lib,include}
+  # remain public. New code should use MacOS::X11.{bin,lib,include}
   # instead, as that accounts for Xcode-only systems.
   def prefix
     @prefix ||= if Pathname.new('/opt/X11/lib/libpng.dylib').exist?