Bump junit from 4.12 to 4.13 (#42)

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

@@ -50,7 +50,7 @@ dependencies {
     compile "io.reactivex:rxjava:1.3.8"
     compile "io.reactivex.rxjava3:rxjava:3.0.0-RC7"
 
-    testCompile group: 'junit', name: 'junit', version: '4.12'
+    testCompile group: 'junit', name: 'junit', version: '4.13'
     testCompile 'org.mockito:mockito-core:3.2.4'
 }