Fix RTMP library gradle file. (GitHub issue #3038)
Fix RTMP library gradle file.
(GitHub issue #3038)

Module prefix was missing for library-core module.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161366375

ened/ExoPlayer,androidx/media,ened/ExoPlayer,google/ExoPlayer,androidx/media,KiminRyu/ExoPlayer,ebr11/ExoPlayer,kiall/ExoPlayer,saki4510t/ExoPlayer,tntcrowd/ExoPlayer,MaTriXy/ExoPlayer,stari4ek/ExoPlayer,androidx/media,superbderrick/ExoPlayer,KiminRyu/ExoPlayer,google/ExoPlayer,ebr11/ExoPlayer,tntcrowd/ExoPlayer,ened/ExoPlayer,KiminRyu/ExoPlayer,kiall/ExoPlayer,google/ExoPlayer,amzn/exoplayer-amazon-port,kiall/ExoPlayer,stari4ek/ExoPlayer,MaTriXy/ExoPlayer,amzn/exoplayer-amazon-port,saki4510t/ExoPlayer,saki4510t/ExoPlayer,tntcrowd/ExoPlayer,MaTriXy/ExoPlayer,stari4ek/ExoPlayer,amzn/exoplayer-amazon-port,ebr11/ExoPlayer,superbderrick/ExoPlayer,superbderrick/ExoPlayer