Session: Fix saving session data on shutdown from project mode

This was broken in d52ee686d1.

Task-number: QTCREATORBUG-13098
Change-Id: Ia075e13fdd00e561b78058a3cab0cb02d2eb5fe6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/modemanager.h

@@ -52,7 +52,7 @@ class CORE_EXPORT ModeManager : public QObject
     Q_OBJECT
 
 public:
-    static QObject *instance();
+    static ModeManager *instance();
 
     static IMode *currentMode();
     static IMode *mode(Id id);