Bump junit from 4.12 to 4.13 (#14)

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>

build.gradle

@@ -27,7 +27,7 @@ repositories {
 dependencies {
     compile gradleApi()
 
-    testCompile group: 'junit', name: 'junit', version: '4.12'
+    testCompile group: 'junit', name: 'junit', version: '4.13'
     testCompile gradleTestKit()
     testCompile ('org.spockframework:spock-core:1.3-groovy-2.5') {
         exclude group:'org.codehaus.groovy'