Bump rxjava from 3.0.13 to 3.1.0 (#119)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 3.0.13 to 3.1.0.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Commits](ReactiveX/RxJava@v3.0.13...v3.1.0)

---
updated-dependencies:
- dependency-name: io.reactivex.rxjava3:rxjava
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

build.gradle

@@ -48,7 +48,7 @@ dependencies {
 
     compile "org.reactivestreams:reactive-streams:1.0.3"
     compile "io.reactivex:rxjava:1.3.8"
-    compile "io.reactivex.rxjava3:rxjava:3.0.13"
+    compile "io.reactivex.rxjava3:rxjava:3.1.0"
 
     testCompile group: 'junit', name: 'junit', version: '4.13.2'
     testCompile 'org.mockito:mockito-core:3.11.2'