Refactor ARGV.kegs

Library/Homebrew/extend/ARGV.rb

@@ -33,21 +33,16 @@ module HomebrewArgvExtension
 
       linked_keg_ref = HOMEBREW_REPOSITORY/"Library/LinkedKegs"/name
 
-      if not linked_keg_ref.symlink?
-        if dirs.length == 1
+      if linked_keg_ref.symlink?
+        Keg.new(linked_keg_ref.realpath)
+      elsif dirs.length == 1
         Keg.new(dirs.first)
-        else
-          prefix = Formula.factory(canonical_name).prefix
-          if prefix.directory?
+      elsif (prefix = Formula.factory(canonical_name).prefix).directory?
         Keg.new(prefix)
       else
         raise MultipleVersionsInstalledError.new(name)
       end
     end
-      else
-        Keg.new(linked_keg_ref.realpath)
-      end
-    end
   rescue FormulaUnavailableError
     if rack
       raise <<-EOS.undent