lcio: Bug in TrackerRawData marshaling

Created by: decibelcooper

I have found that TrackerRawData hits are not handled correctly in lcio. For example, see https://github.com/go-hep/hep/blob/master/lcio/trackerrawdata.go#L94 compared to https://github.com/iLCSoft/LCIO/blob/master/src/java/hep/lcio/implementation/sio/SIOTrackerRawData.java#L26

I have written a fix and will point a pull request here. Please excuse my inexperience with Go.

P.S. Thanks for your great work