Clarify that only nonprimary extensions should be sorted

test/test_pedantic.rb

@@ -9,7 +9,7 @@ class TestPedantic < Minitest::Test
     assert_sorted LANGUAGES.keys
   end
 
-  def test_extensions_are_sorted
+  def test_nonprimary_extensions_are_sorted
     LANGUAGES.each do |name, language|
       extensions = language['extensions']
       assert_sorted extensions[1..-1].map(&:downcase) if extensions && extensions.size > 1