Change to xpra version 0.11.6 as 0.12.5 was not working
Change to xpra version 0.11.6 as 0.12.5 was not working

Version 0.11.6 was the latest version that I was able to get building
and running on NixOS. Unfortunately my previous commit for 0.12.5 was
an error and incomplete.

SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,triton/triton,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs