Deprecate EntryEndpoint.entry_translations

Oxford Dictionaries is updating their API to a new version which
includes quite a few changes:
https://developer.oxforddictionaries.com/version2

They are moving the translations functionality to its own endpoint
(instead of having part of the entries endpoint).

lib/oxford_dictionary/endpoints/entry_endpoint.rb

@@ -48,6 +48,13 @@ def entry_antonyms_synonyms(query, params = {})
       end
 
       def entry_translations(query, params = {})
+        warn '''
+        Client#entry_translations is DEPRECATED and will become non-functional
+        on June 30, 2019. Use Client#translation instead. Reference
+        https://github.com/swcraig/oxford-dictionary/pull/12 for more
+        information. Check out OxfordDictionary::Endpoints::Translations for the
+        interface to use.
+        '''
         params.key?(:translations) || params[:translations] = 'es'
         entry_request(query, params)
       end