Add default touch detect threshold

TFT_eSPI.h

@@ -484,7 +484,7 @@ class TFT_eSPI : public Print {
   uint32_t lastColor = 0xFFFF;
 
            // These are associated with the Touch Screen handlers
-  uint8_t  validTouch(uint16_t *x, uint16_t *y, uint16_t threshold);
+  uint8_t  validTouch(uint16_t *x, uint16_t *y, uint16_t threshold = 600);
            // Initialise with example calibration values so processor does not crash if setTouch() not called in setup()
   uint16_t touchCalibration_x0 = 300, touchCalibration_x1 = 3600, touchCalibration_y0 = 300, touchCalibration_y1 = 3600;
   uint8_t  touchCalibration_rotate = 1, touchCalibration_invert_x = 2, touchCalibration_invert_y = 0;