v0.12.1 GTFS+ GTFS-RT robustness

Please check on your GTFS feeds that the new GTFS-RT matching logic still works.

What's Changed

• update nigiri - fixes #501 by @felixguendling in #502

Improvements:

• handling of special case "only one agency" = "routes.txt can omit agency info" (important for timezone)
• handling of ambiguous start_time GTFS-RT attribute 24:15:00 is the same as 00:15:00 on the next day
• improved interval extension logic

Full Changelog: v0.12.0...v0.12.1