Bump rxjava from 2.2.12 to 2.2.13 (#4)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 2.2.12 to 2.2.13.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Changelog](https://github.com/ReactiveX/RxJava/blob/v2.2.13/CHANGES.md)
- [Commits](ReactiveX/RxJava@v2.2.12...v2.2.13)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

build.gradle

@@ -49,7 +49,7 @@ repositories {
 }
 
 dependencies {
-    implementation "io.reactivex.rxjava2:rxjava:2.2.12"
+    implementation "io.reactivex.rxjava2:rxjava:2.2.13"
     implementation "io.reactivex.rxjava3:rxjava:3.0.0-RC3"
     testImplementation 'junit:junit:4.12'
 }