Update the ExternalProjectsContrib repo hash to the latest master

CMakeLists.txt

@@ -832,7 +832,7 @@ if(CTK_USE_CONTRIBUTED_PLUGINS)
     ctkFunctionCheckoutRepo(
       NAME ExternalProjectsContrib
       GIT_URL github.com/commontk/ExternalProjectsContrib.git
-      GIT_TAG 97dcdc261b
+      GIT_TAG c15781914f
       )
   endif()