fix for Task-2-Buttons

Hi, I noticed the Task-2-Buttons project didn't work. I believe the LED's are on GPIOD, not GPIOA. I also made it more like the project evolved from Task-1-Leds. When the user presses the button, the 'next' LED lights up.

This is my first pull request. Hope I'm doing it right. Please be gentle :)

Thanks!

	modified:   Task-2-Buttons/inc/main.h
	modified:   Task-2-Buttons/src/main.c