Bump junit from 4.12 to 4.13 (#13)

Bumps [junit](https://github.com/junit-team/junit4) from 4.12 to 4.13.
- [Release notes](https://github.com/junit-team/junit4/releases)
- [Changelog](https://github.com/junit-team/junit4/blob/master/doc/ReleaseNotes4.12.md)
- [Commits](junit-team/junit4@r4.12...r4.13)

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

Author: dependabot-preview[bot]

build.gradle

@@ -44,7 +44,7 @@ repositories {
 
 dependencies {
     implementation "io.reactivex.rxjava3:rxjava:3.0.0-RC7"
-    testImplementation 'junit:junit:4.12'
+    testImplementation 'junit:junit:4.13'
     testImplementation "org.reactivestreams:reactive-streams-tck:1.0.3"
     testImplementation "org.testng:testng:7.1.0"
     testImplementation "com.beust:jcommander:1.78"