Bump rxjava from 3.0.0-RC7 to 3.0.0-RC8 (#9)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 3.0.0-RC7 to 3.0.0-RC8.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Commits](ReactiveX/RxJava@v3.0.0-RC7...v3.0.0-RC8)

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

Author: dependabot-preview[bot]

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-	ext.rxjavaVersion = "3.0.0-RC7"
+	ext.rxjavaVersion = "3.0.0-RC8"
 	ext.rxjavaDocVersion = "3.x"
 	ext.licenseVersion = "0.15.0"
 	ext.animalSnifferVersion = "1.5.0"