Changed `CONFLICT` to `SQL` for multiline strings

This is more consistent with the rest of our codebase.

app/models/topic_group.rb

@@ -49,10 +49,10 @@ class TopicGroup < ActiveRecord::Base
 
     query += 'AND NOT(tag.group_id IN (:already_updated_groups))' unless updated_group_ids.length.zero?
 
-    query += <<~CONFLICT
+    query += <<~SQL
       ON CONFLICT(topic_id, group_id)
       DO UPDATE SET last_read_post_number = :post_number, created_at = :now, updated_at = :now
-    CONFLICT
+    SQL
 
     DB.exec(
       query,