What is hidden behind this chevron?
If you clap that open, we can see what device OS version you are targeting
But I think there was a poor choice in that library to use KEY_H as guard against multi inclusion since KEY_H is already taken by the USBKeyboard key map for the H key.
The compiler doesn’t really like redefinitions of that kind 
You’ll probably need to copy/paste the code of that library into your own project, change that definition and try again.
You could also file a GitHub issue on the library (providing it’s still maintained by the original contributor).
Update:
I just checked and there already is such an issue filed
and even a PR to solve that issue, but the contributor hasn’t picked up on that since June 2017