brew doctor recommends using cask to upgrade XQuartz

Also changes exceptions.rb to use Formatter.url

Library/Homebrew/cask/lib/hbc/exceptions.rb

@@ -84,13 +84,11 @@ module Hbc
   class CaskX11DependencyError < AbstractCaskErrorWithToken
     def to_s
       <<-EOS.undent
-        #{token} requires XQuartz/X11, which can be installed via homebrew-cask by
-
+        #{token} requires XQuartz/X11, which can be installed using Homebrew-Cask by running
           brew cask install xquartz
 
         or manually, by downloading the package from
-
-          https://www.xquartz.org/
+          #{Formatter.url("https://www.xquartz.org/")}
       EOS
     end
   end

Library/Homebrew/extend/os/mac/diagnostic.rb

@@ -264,8 +264,9 @@ module Homebrew
 
         <<-EOS.undent
           Your XQuartz (#{installed_version}) is outdated.
-          Please install XQuartz #{latest_version} (or delete it):
-            https://xquartz.macosforge.org
+          Please install XQuartz #{latest_version} (or delete the current version).
+          XQuartz can be updated using Homebrew-Cask by running
+            brew cask reinstall xquartz
         EOS
       end