If there is no transformation.txt file with your GTFS data the GTFSImporter stops with an error...

[michalKopec]

Easy way to fix it was to add a dummy, empty transformations.txt to the directory with other GTFS files.

[jogi]

The easiest way is to comment this line out - https://github.com/jvashishtha/GTFSImporter/blob/master/GTFSImporter/main.m#L51