Bump exoplayer from 2.15.0 to 2.15.1

Bumps [exoplayer](https://github.com/google/ExoPlayer) from 2.15.0 to 2.15.1.
- [Release notes](https://github.com/google/ExoPlayer/releases)
- [Changelog](https://github.com/google/ExoPlayer/blob/release-v2/RELEASENOTES.md)
- [Commits](https://github.com/google/ExoPlayer/compare/r2.15.0...r2.15.1)

---
updated-dependencies:
- dependency-name: com.google.android.exoplayer:exoplayer
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

app/build.gradle

@@ -275,7 +275,7 @@ dependencies {
     implementation "com.afollestad.material-dialogs:lifecycle:${materialDialogsVersion}"
 
     implementation 'com.google.code.gson:gson:2.8.8'
-    implementation 'com.google.android.exoplayer:exoplayer:2.15.0'
+    implementation 'com.google.android.exoplayer:exoplayer:2.15.1'
 
     implementation 'com.github.chrisbanes:PhotoView:2.3.0'
     implementation 'pl.droidsonroids.gif:android-gif-drawable:1.2.23'