Building with GTK < 3.22

[Paul Clarke <paulclarke345 gmail com>]

Hello,
I've been using Deja Dup for a while, and was thinking about helping out with some of the outstanding bugs. It works great on my system, which is linux mint with gtk 3.18.9.

When I tried to build it, though, meson told me it requires gtk >= 3.22, which my os doesn't have a package for, and would probably be a pain to compile from source. Is gtk 3.22 really required for development, or is there an easy way to turn off that dependency? Thanks,

Paul.