Use Int64 for fts_targets.tag_ids
Use Int64 for fts_targets.tag_ids

Because Active Record 5 uses bigint (64bit integer) for id. Active
Record 4 uses int (32bit integer) for id but we don't support Active
Record 4. So we can always use Int64 for fts_targets.tag_ids.

okkez/redmine_full_text_search,okkez/redmine_full_text_search