Issue #10: Force millisecond label to update just before we grab video image.

sksurgeryvideolag/ui/sksurgeryvideolag_demo.py

@@ -106,6 +106,10 @@ class DemoGui(QtWidgets.QWidget):
     @Slot()
     def update_image(self):
         """Updates the image."""
+
+        # Force updating the GUI to get the latest possible time.
+        self.text.update()
+
         start_time = time.time()
 
         # Then grab image