Bump mockito-core from 2.23.0 to 2.23.4 (#4502)

Bumps [mockito-core](https://github.com/mockito/mockito) from 2.23.0 to 2.23.4.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](mockito/mockito@v2.23.0...v2.23.4)

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

build.gradle

@@ -168,7 +168,7 @@ dependencies {
     testCompile 'org.junit-pioneer:junit-pioneer:0.3.0'
     testRuntime 'org.apache.logging.log4j:log4j-core:2.11.1'
     testRuntime 'org.apache.logging.log4j:log4j-jul:2.11.1'
-    testCompile 'org.mockito:mockito-core:2.23.0'
+    testCompile 'org.mockito:mockito-core:2.23.4'
     testCompile 'com.github.tomakehurst:wiremock:2.19.0'
     testCompile 'org.assertj:assertj-swing-junit:3.8.0'
     testCompile 'org.reflections:reflections:0.9.11'