title: maven git-commit-id-plugin: commitId of subfolder/submodule
body: <p>I'm using the <code>maven-git-commit-id-plugin</code> maven plugin to get data like commitId. My maven project has some submodules in subfolders, like this:</p>
  
  <pre><code>hfe/pom.xml -
              - backend/pom.xml
              - frontend/pom.xml
  </code></pre>
  
  <p><code>hfe</code> is the git-checkout, so there the folder .git exists. </p>
  
  <p>In <code>hfe/pom.xml</code> in the build section I add the <code>maven-git-commit-id-plugin</code> so that it will be executed in every submodule.</p>
  
  <p>If I do now a <code>mvn package</code> in the folder <code>hfe/backend/</code>, I will get the latest commitId of the whole project in the generated git-property-file. Is it possible to get the latest commitId of the subfolder hfe/backend.</p>
  
  <p>To make it clear, I would like to have the commitId 90791bcf... in the file hfe/backend/target/git.properties, but in the moment I get the commitId d022a39342...:</p>
  
  <pre><code>/projects/hfe&gt;git log -n 1 backend
  commit 90791bcf145ee635c61f25c0ac62d0d66c49307f
  Author: me
  Date:   Fri May 10 12:30:31 2019 +0200
  
  /projects/hfe&gt;git log -n 1
  commit d022a39342ecd6bcedeafbaf4bd80db495fdf23c (HEAD -&gt; master, origin/master, origin/HEAD)
  Author: other
  Date:   Sun May 12 21:58:50 2019 +0200
  </code></pre>
  
  <p>Maybe there is another maven plugin which can do this?</p>