more explicit force bug fix mention in release notes

Author: WolfgangWaltenberger

ReleaseNotes

@@ -5,7 +5,7 @@ Release v3.1.1
   Wuerzinger for reporting this)
   * added filter for slogdet warnings (relevant on MacOS)
   * Minor fixes in slha printer
-  * Bumped up pythia8 from 8315 to 8317
+  * Bumped up pythia8 from 8315 to 8317 (fixes "force" bug)
   * Fixed bug preventing the extended output to be printed
   * Added final states information to output
   * Fix for pyslha 3.3.1