Fix build on Qt 5.5

Author: MKleusberg

src/MainWindow.cpp

@@ -3759,7 +3759,11 @@ TableBrowserDock* MainWindow::newTableBrowserTab(const sqlb::ObjectIdentifier& t
     // Set up dock and add it to the tab
     ui->tabBrowsers->addDockWidget(Qt::TopDockWidgetArea, d);
     if(allTableBrowserDocks().size() > 1)
+#if QT_VERSION < QT_VERSION_CHECK(5, 6, 0)
+        ui->tabBrowsers->tabifyDockWidget(allTableBrowserDocks().front(), d);
+#else
         ui->tabBrowsers->tabifyDockWidget(allTableBrowserDocks().constFirst(), d);
+#endif
 
     // Set current model and browser
     d->activateWindow();