extend/fileutils: fix Rubocop warnings.

Library/Homebrew/extend/fileutils.rb

@@ -60,10 +60,10 @@ module FileUtils
       # > When a new file is created, it is given the group of the directory which
       # contains it.
       group_id = if HOMEBREW_BREW_FILE.grpowned?
-                   HOMEBREW_BREW_FILE.stat.gid
-                 else
-                   Process.gid
-                 end
+        HOMEBREW_BREW_FILE.stat.gid
+      else
+        Process.gid
+      end
       begin
         chown(nil, group_id, tmpdir)
       rescue Errno::EPERM