Json.hpp needed for aarch64 and armv6l

[ofTheo]

Currently both of the RPI / linux arm nightly builds don't include Json.hpp

0.12.0 included it, so given that only the ubuntu install script is adding the package and Jetson Nano doesn't seem to have it ( see: openframeworks/openFrameworks#8389 ), it might be good to include it the same way we did for 0.12.0

cc @danoli3