Bump application version to v.1.38.1.
Bump application version to v.1.38.1.

+ Skipping versionCode 51 to align with F-Droid release.
  See: https://gitlab.com/fdroid/fdroiddata/blob/master/metadata/info.metadude.android.congress.schedule.yml#L112

EventFahrplan/EventFahrplan,EventFahrplan/EventFahrplan