Bump junit from 4.13 to 4.13.1

Bumps [junit](https://github.com/junit-team/junit4) from 4.13 to 4.13.1.
- [Release notes](https://github.com/junit-team/junit4/releases)
- [Changelog](https://github.com/junit-team/junit4/blob/main/doc/ReleaseNotes4.13.1.md)
- [Commits](junit-team/junit4@r4.13...r4.13.1)

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

agent/build.gradle

@@ -59,7 +59,7 @@ dependencies {
     compileOnly 'io.reactivex.rxjava2:rxjava:2.2.18'
 
     jarFileTestCompile 'org.assertj:assertj-core:3.18.1'
-    jarFileTestCompile 'junit:junit:4.13'
+    jarFileTestCompile 'junit:junit:4.13.1'
 }
 
 task sourcesJar(type: Jar) {

example/build.gradle

@@ -45,7 +45,7 @@ dependencies {
     testCompile 'io.projectreactor:reactor-core:3.2.2.RELEASE'
     testCompile 'io.reactivex.rxjava2:rxjava:2.2.18'
 
-    testCompile 'junit:junit:4.13'
+    testCompile 'junit:junit:4.13.1'
     testCompile 'org.assertj:assertj-core:3.18.1'
 
     reactor_3_3_x 'io.projectreactor:reactor-core:3.3.0.RC1'