Keep line numbers when running proguard.
Keep line numbers when running proguard.

- Better logs for Crashlytics.

UweTrottmann/SeriesGuide,r00t-user/SeriesGuide,0359xiaodong/SeriesGuide,epiphany27/SeriesGuide,artemnikitin/SeriesGuide,hoanganhx86/SeriesGuide,UweTrottmann/SeriesGuide