Coding style fix

Our coding style says that private properties should end with an underscore,
lets make it so.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/Kaleidoscope-LEDEffect-Breathe.cpp

@@ -20,9 +20,9 @@
 namespace kaleidoscope {
 void LEDBreatheEffect::update(void) {
   uint16_t now = millis();
-  if ((now - last_update) < UPDATE_INTERVAL)
+  if ((now - last_update_) < UPDATE_INTERVAL)
     return;
-  last_update = now;
+  last_update_ = now;
 
   cRGB color = breath_compute(hue, saturation);
   ::LEDControl.set_all_leds_to(color);

src/Kaleidoscope-LEDEffect-Breathe.h

@@ -31,7 +31,7 @@ class LEDBreatheEffect : public LEDMode {
   void update(void) final;
 
  private:
-  uint16_t last_update = 0;
+  uint16_t last_update_ = 0;
 };
 }