chore(deps): bump rxjava from 2.2.14 to 2.2.15 (#2439)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 2.2.14 to 2.2.15.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Changelog](https://github.com/ReactiveX/RxJava/blob/v2.2.15/CHANGES.md)
- [Commits](ReactiveX/RxJava@v2.2.14...v2.2.15)

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

Author: dependabot-preview[bot]

app/build.gradle

@@ -208,7 +208,7 @@ dependencies {
     // RxJava
     implementation 'io.reactivex.rxjava2:rxandroid:2.1.1'
     implementation 'io.reactivex.rxjava2:rxkotlin:2.4.0'
-    implementation 'io.reactivex.rxjava2:rxjava:2.2.14'
+    implementation 'io.reactivex.rxjava2:rxjava:2.2.15'
     implementation 'com.squareup.retrofit2:adapter-rxjava2:2.6.2'
 
     // Picasso