Bump wiremock from 2.20.0 to 2.21.0 (#4623)

Bumps [wiremock](https://github.com/tomakehurst/wiremock) from 2.20.0 to 2.21.0.
- [Release notes](https://github.com/tomakehurst/wiremock/releases)
- [Changelog](https://github.com/tomakehurst/wiremock/blob/master/release-settings.gradle)
- [Commits](wiremock/wiremock@2.20.0...2.21.0)

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

build.gradle

@@ -171,7 +171,7 @@ dependencies {
     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:2.23.4'
-    testCompile 'com.github.tomakehurst:wiremock:2.20.0'
+    testCompile 'com.github.tomakehurst:wiremock:2.21.0'
     testCompile 'org.assertj:assertj-swing-junit:3.8.0'
     testCompile 'org.reflections:reflections:0.9.11'
     testCompile 'org.xmlunit:xmlunit-core:2.6.2'