Added support for overriding merge message for the gitflow:release-finish on develop branch

[pcoulso1]

Most of the git commit messages can now be overridden, however one during gitflow:release-finish cannot.

Our git commit hooks require a ticket to be listed against all commits. This one merge message prevents us from using this plugin.

Proposed solution

Use the releaseFinishMergeMessage for the one commit message which cannot be overridern

e.g. within src/main/java/com/amashchenko/maven/plugin/gitflow/GitFlowReleaseFinishMojo.java at line 281 modify the code from

// merge branch master into develop gitMerge(releaseBranch, releaseRebase, releaseMergeNoFF, false, null, null);

to

// merge branch master into develop gitMerge(releaseBranch, releaseRebase, releaseMergeNoFF, false, commitMessages.getReleaseFinishMergeMessage(), messageProperties);

[aleksandr-m]

@pcoulso1 1.13.0 is out.