Ignore meta json in subdir

Currently, META.json precedes META.yml unconditionally. This is usually ok as both META.json and META.yml are usually located in the top directory, but I found a (rare) case (Test::Module::Used 0.2.4) where META.json is located in a subdirectory and only META.yml is located in the top directory. In this case, META.yml should have precedence.