Specify acts_as_searchable :references in Meeting

See core commit:
c02804b0eb

Signed-off-by: Alex Coles <alex@alexbcoles.com>

app/models/meeting.rb

@@ -43,6 +43,7 @@ class Meeting < ActiveRecord::Base
 
   acts_as_searchable columns: ["#{table_name}.title", "#{MeetingContent.table_name}.text"],
                      include: [:contents, :project],
+                     references: :meeting_contents,
                      date_column: "#{table_name}.created_at"
 
   acts_as_journalized