Bump rxjava from 3.0.0-RC2 to 3.0.0-RC3 (#9)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 3.0.0-RC2 to 3.0.0-RC3.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Commits](ReactiveX/RxJava@v3.0.0-RC2...v3.0.0-RC3)

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

build.gradle

@@ -4,7 +4,7 @@ buildscript {
     // Versions
     // ------------------------------------------------------------------
 
-    ext.rxjava3Version = "3.0.0-RC2"
+    ext.rxjava3Version = "3.0.0-RC3"
     ext.rxjava3DocVersion = "3.x"
     ext.licenseVersion = "0.15.0"
     ext.animalSnifferVersion = "1.5.0"