Bump ExoPlayer to 2.10.8

Here we go again.
Minor update.
ExoPlayer Changelog: https://github.com/google/ExoPlayer/blob/release-v2/RELEASENOTES.md

app/build.gradle

@@ -47,7 +47,7 @@ android {
 
 ext {
     androidxLibVersion = '1.0.0'
-    exoPlayerLibVersion = '2.10.7'
+    exoPlayerLibVersion = '2.10.8'
     roomDbLibVersion = '2.1.0'
     leakCanaryLibVersion = '1.5.4' //1.6.1
     okHttpLibVersion = '3.12.6'