Prepare release 3.1.6

Author: Godin

org.eclipse.eclemma.doc/pages/changes.html

@@ -11,7 +11,7 @@
 
 <h1>EclEmma Change Log</h1>
 
-<h2>Version 3.1.6 (not yet released)</h2>
+<h2>Version 3.1.6 (2022/06/01)</h2>
 <ul>
   <li>Improve interoperability with other launchers which delegate to EclEmma coverage launchers.
       Contributed by Lukas Pecak (GitHub <a href="https://github.com/eclipse/eclemma/pull/28">#28</a>).</li>