Add dev-dependency for extern time library
Add dev-dependency for extern time library

Fixes a deprecation warning, see:
https://github.com/rust-lang/rust/commit/fcd05ed99ff0aa6157e427a698ac53dbc450135f

aepsil0n/gfx-rs,tempbottle/gfx,alexcrichton/gfx,ColinKinloch/gfx,gfx-rs/gfx-rs,JohnColanduoni/gfx,tanderegg/gfx,sectopod/gfx-rs,JohnColanduoni/gfx,tanderegg/gfx,mitchmindtree/gfx-rs,davll/gfx,Bastacyclop/gfx,red75prime/gfx,bvssvni/gfx-rs,ColinKinloch/gfx