purple-matrix: 2016-07-11 -> 2018-08-02

[symphorien]

This also fixes the build.

Motivation for this change

The build was broken. This probably should be backported to 18.09. Should I open another PR for this ?

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

I tested the plugin with pidgin, it works, except that icons seem to be ignored for some reason.

[symphorien]

cc #45960

[vcunat]

Backported, too.