Travis: build on both nightly and beta
Travis: build on both nightly and beta

insanebits/gtk,rust-gnome/gtk,drewet/gtk,LordSentox/gtk,daa84/gtk,rust-gnome/gtk,gkoz/gtk-rs-gtk,insanebits/gtk,Susurrus/gtk,gkoz/rust-gnome-gtk,EPashkin/rust-gnome-gtk,EPashkin/rust-gnome-gtk,drewet/gtk,gkoz/gtk-rs-gtk,daa84/gtk,gkoz/rust-gnome-gtk,Susurrus/gtk,mitaa/gtk,LordSentox/gtk,mitaa/gtk