lang/mono: Update to 4.0.3.19

[Anders Jensen-Waud]

Hi all,

Please note that I have submitted a patch, which updates Mono to 
4.0.3.19 in Ports.

The patch is available as a PR here, but has been left untouched for 
quite a while:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=201883

If there is no interest in maintaining this port, I am willing to put my 
hand up to become the port maintainer going forward. We are still 
working on finalising the porting effort of CoreCLR and Roslyn to 
FreeBSD, and an up to date Mono is critical to make this possible.

Thanks,

Anders