Merge pull request #7567 from zachauten/cask-help-exception

Fix exception when calling "brew cask" with --help and no subcommand

Library/Homebrew/cask/cmd.rb

@@ -243,6 +243,10 @@ module Cask
         $stderr.puts
         $stderr.puts Help.usage
       end
+
+      def help
+        run
+      end
     end
   end
 end