Bump gson from 2.9.0 to 2.9.1

Bumps [gson](https://github.com/google/gson) from 2.9.0 to 2.9.1.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/gson/compare/gson-parent-2.9.0...gson-parent-2.9.1)

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

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

app/build.gradle

@@ -293,7 +293,7 @@ dependencies {
     implementation "com.afollestad.material-dialogs:bottomsheets:${materialDialogsVersion}"
     implementation "com.afollestad.material-dialogs:lifecycle:${materialDialogsVersion}"
 
-    implementation 'com.google.code.gson:gson:2.9.0'
+    implementation 'com.google.code.gson:gson:2.9.1'
     implementation 'com.google.android.exoplayer:exoplayer:2.18.1'
 
     implementation 'com.github.chrisbanes:PhotoView:2.3.0'