Press the big red button on PlatformIO 4.0

platformio.ini

 lib_dir      = .piolib
 libdeps_dir  = .piolibdeps
 boards_dir   = buildroot/share/PlatformIO/boards
-env_default  = megaatmega2560
+default_envs = megaatmega2560
 
 [common]
 default_src_filter = +<src/*> -<src/config> -<src/HAL> +<src/HAL/shared>