Updates from 3rdparty/plutovg

[ivantishchenko]

It seems that there is a fork of this library inside lunasvg. Should the changes from the fork be applied here? This way this library can be used as a submodule in https://github.com/sammycage/lunasvg.

https://github.com/sammycage/lunasvg/tree/master/3rdparty/plutovg