[BUG] Credentials helpers assumed to return a version number

[giannello]

Description

Starting with 0.23, docker-maven-plugin supports docker credential helpers. By default, they are called with the version argument to get the plugin version and use it in a log message.
Not all the helpers, however, return a version number when called with the version argument (tested with docker-credential-gcloud here, part of google-cloud-sdk).

Info

• d-m-p version: 0.23.0

[giannello]

@rhuss any chance to get the PR merged? This bug comes from a wrong assumption about the helpers' behavior, so it makes sense to make the version check optional.

[rhuss]

@giannello thanks for the PR, to make a PR integration sweep this weekend (constantly overloaded with 'regular' work at the moment). If I get to it, I will make a new release, too then.

thanks for your contribution ....