List new changes-2.3.1 file in qtcreator.pro

Change-Id: I611935b4c993d70a566fe1cbc6bcf5eb362339c2
Reviewed-on: http://codereview.qt.nokia.com/4349

Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

qtcreator.pro

@@ -25,4 +25,5 @@ OTHER_FILES += dist/copyright_template.txt \
     dist/changes-2.0.1 \
     dist/changes-2.1.0 \
     dist/changes-2.2.0 \
-    dist/changes-2.3.0
+    dist/changes-2.3.0 \
+    dist/changes-2.3.1