Update wiremock and wiremock extension-convention plugin

[zyberzebra]

Update wiremock and wiremock extension-convention plugin

References

• https://github.com/wiremock/gradle-wiremock-extension-plugins/releases/tag/0.4.0

Submitter checklist

• Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
• The PR request is well described and justified, including the body and the references
• The PR title represents the desired changelog entry
• The repository's code style is followed (see the contributing guide)
• Test coverage that demonstrates that the change works as expected
• For new features, there's necessary documentation in this pull request or in a subsequent PR to wiremock.org

[RafeArnold]

superceded by #20