Update dependencies in the apps metadata plugin

[onobc]

Some of the dependencies in the Apps metadata and docs generator plugin used by the stream-applications need to be updated.

One example, is where our good friend dependa-bot recently created these to update Maven:

• https://github.com/spring-cloud/stream-applications/pull/491
• https://github.com/spring-cloud/stream-applications/pull/490

After the 4.x release, let's update the plugins dependencies across the board.