You’re giving it the wrong git link. Must be the one you get when you go to “Clone or download” in the upper right corner.
https://github.com/clplaneguy/Makeblock-Robot.git
Select the wanted branch name by adding a #branchname
or #commithash
at the end, as e.g. seen in Howto use dedicated stage version · Issue #49 · platformio/platform-espressif8266 · GitHub