Find Gemfile.lock before gems.locked

Generally named Gemfile.lock instead of gems.locked. So finding in gems.locked
is redundant most of the time.

There was once a proposal to deprecate Gemfile and become gems.rb in
past Bundler 2 development, but that has been abandoned.

lib/rubocop/config.rb

@@ -242,7 +242,7 @@ def bundler_lock_file_path
       return nil unless loaded_path
 
       base_path = base_dir_for_path_parameters
-      ['gems.locked', 'Gemfile.lock'].each do |file_name|
+      ['Gemfile.lock', 'gems.locked'].each do |file_name|
         path = find_file_upwards(file_name, base_path)
         return path if path
       end