Fix missing method in test

Author: eizengan

lib/slack/web/api/mixins/conversations.id.rb

@@ -16,14 +16,15 @@ def conversations_id(options = {})
             name = options[:channel]
             raise ArgumentError, 'Required arguments :channel missing' if name.nil?
 
+            limit = respond_to?(:conversations_id_page_size) ? conversations_id_page_size : 100
             id_for(
               :channel,
               name,
               '#',
               :conversations_list,
               :channels,
               'channel_not_found',
-              enum_method_options: { limit: conversations_id_page_size }
+              enum_method_options: { limit: limit }
             )
           end
         end