Clarify that only nonprimary extensions should be sorted

lib/linguist/languages.yml

@@ -8,7 +8,8 @@
 #                     Use "text" if a mode does not exist.
 # wrap              - Boolean wrap to enable line wrapping (default: false)
 # extensions        - An Array of associated extensions (the first one is
-#                     considered the primary extension)
+#                     considered the primary extension, the others should be
+#                     listed alphabetically)
 # interpreters      - An Array of associated interpreters
 # searchable        - Boolean flag to enable searching (defaults to true)
 # search_term       - Deprecated: Some languages maybe indexed under a

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