Small Slope On Square Wave Generator Output
Try adding a second capacitor between VCC and GND to further stabilize the supply, 100µF should do
Add a low-pass filter to the output thats not deforming your signal too much but filters out that annoying peak. 100nF and ~50Ohms should do the trick and not deform your signal too much. If it rounds your squarewaves corners too much you can try to use a smaller cap (22nF) or smaller resistor.