Bump rxjava from 3.0.0-RC3 to 3.0.0-RC4 (#5)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 3.0.0-RC3 to 3.0.0-RC4.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Commits](ReactiveX/RxJava@v3.0.0-RC3...v3.0.0-RC4)

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

Author: dependabot-preview[bot]

build.gradle

@@ -50,7 +50,7 @@ repositories {
 
 dependencies {
     implementation "io.reactivex.rxjava2:rxjava:2.2.13"
-    implementation "io.reactivex.rxjava3:rxjava:3.0.0-RC3"
+    implementation "io.reactivex.rxjava3:rxjava:3.0.0-RC4"
     testImplementation 'junit:junit:4.12'
 }