one less block in mac dep

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

 class DependencyCollector
   def ant_dep(spec, tags)
-    if MacOS.version >= :mavericks
-      Dependency.new(spec.to_s, tags)
-    end
+    return if MacOS.version < :mavericks
+    Dependency.new(spec.to_s, tags)
   end
 end