Rename AvailableLocales.available_locales method

I'm not sure whether we should rename the class instead. I'm renaming
the method because renaming the class would require more changes.

spec/lib/remote_translations/microsoft/available_locales_spec.rb

@@ -1,12 +1,12 @@
 require "rails_helper"
 
 describe RemoteTranslations::Microsoft::AvailableLocales do
-  describe ".available_locales" do
+  describe ".locales" do
     it "includes locales with the same format as I18n.available_locales" do
       allow(RemoteTranslations::Microsoft::AvailableLocales).to receive(:remote_available_locales)
                                                             .and_return(%w[de en es fr pt zh-Hans])
 
-      available_locales = RemoteTranslations::Microsoft::AvailableLocales.available_locales
+      available_locales = RemoteTranslations::Microsoft::AvailableLocales.locales
       expect(available_locales).to eq %w[de en es fr pt-BR zh-CN]
     end
   end