Clean up the CI stuff

[ingorichtsmeier]

What should we do?

Currently, there is a warning in the build:

  Warning:  Some problems were encountered while building the effective model for com.example.workflow:sample-process-solution:jar:1.0.1-SNAPSHOT
  Warning:  'build.plugins.plugin.version' for org.apache.maven.plugins:maven-enforcer-plugin is missing. @ line 111, column 15
  Warning:  
  Warning:  Some problems were encountered while building the effective model for com.example.workflow:sample-process-solution-migrated:jar:1.0.0-SNAPSHOT
  Warning:  'build.plugins.plugin.version' for org.apache.maven.plugins:maven-enforcer-plugin is missing. @ line 105, column 15
  Warning:  
  Warning:  It is highly recommended to fix these problems because they threaten the stability of your build.
  Warning:  
  Warning:  For this reason, future Maven versions might no longer support building such malformed projects.

This should be fixed.

The version of the sample-process-solution was increased to 1.0.1-SNAPSHOT in the last release.

Why should we do it?

Keep consistent examples decoupled from the version of the libraries.

[ingorichtsmeier]

closed with #171