Fix code style - add missing trailing comma

For better consistency and git changes tracking add trailing comma at
the end of the last value of an enum.
See also code-review at:
https://codereview.qt-project.org
/c/qt/qtbase/+/528392/comment/663ba25a_51ed514b/

Change-Id: Ibcfcfb1ba1a8ba4b59297bf17103181a0ee6eafc
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit afa6cbed649add8abcef7f07e97e83b16983ff16)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/io/qstandardpaths.h

@@ -40,7 +40,7 @@ public:
         PublicShareLocation,
         TemplatesLocation,
         StateLocation,
-        GenericStateLocation
+        GenericStateLocation,
     };
     Q_ENUM(StandardLocation)