Build(deps): Bump com.google.android.exoplayer:exoplayer

Bumps [com.google.android.exoplayer:exoplayer](https://github.com/google/ExoPlayer) from 2.18.6 to 2.18.7.
- [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/r2.18.6...r2.18.7)

---
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

@@ -262,7 +262,7 @@ dependencies {
     implementation "com.afollestad.material-dialogs:lifecycle:${materialDialogsVersion}"
 
     implementation 'com.google.code.gson:gson:2.10.1'
-    implementation 'com.google.android.exoplayer:exoplayer:2.18.6'
+    implementation 'com.google.android.exoplayer:exoplayer:2.18.7'
 
     implementation 'com.github.chrisbanes:PhotoView:2.3.0'
     implementation 'pl.droidsonroids.gif:android-gif-drawable:1.2.25'