Bump converter-gson from 2.4.0 to 2.9.0

Bumps [converter-gson](https://github.com/square/retrofit) from 2.4.0 to 2.9.0.
- [Release notes](https://github.com/square/retrofit/releases)
- [Changelog](https://github.com/square/retrofit/blob/master/CHANGELOG.md)
- [Commits](square/retrofit@parent-2.4.0...2.9.0)

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

app/build.gradle

@@ -98,7 +98,7 @@ dependencies {
     implementation 'com.github.jkwiecien:EasyImage:1.3.1'
     implementation 'com.facebook.device.yearclass:yearclass:2.0.0'
     implementation 'com.squareup.retrofit2:retrofit:2.4.0'
-    implementation 'com.squareup.retrofit2:converter-gson:2.4.0'
+    implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
     implementation 'com.squareup.retrofit2:adapter-rxjava:2.9.0'
     implementation 'com.squareup.okhttp3:logging-interceptor:3.11.0'
     implementation 'io.reactivex:rxjava:1.3.0'