dependency on GTK not tight enough

Originally filed at https://bugzilla.gnome.org/show_bug.cgi?id=673331 but still valid from what I can see in meson.build:

libgtk = dependency('gtk+-3.0', version : '>= 2.91.0')

According to configure.ac, gtk+-3.0 >= 2.91.0 should be sufficient. Compiling gnome-color-manager with GTK 3.2, I get

gcm_viewer-gcm-viewer.o: In function gcm_viewer_startup_cb': /tmp/buildd/gnome-color-manager-3.4.0/src/gcm-viewer.c:1465: undefined reference to gtk_builder_add_from_resource' collect2: ld returned 1 exit status

Looks like the dependency needs to be bumped. I think it was added in c72a76c754e75d9c03db1030f96393fc385c648e, i.e 3.3.8