nix: Bump rust to 1.31.1 in gecko_env (#1781)
nix: Bump rust to 1.31.1 in gecko_env (#1781)


La0/mozilla-relengapi,La0/mozilla-relengapi,mozilla-releng/services,mozilla-releng/services,La0/mozilla-relengapi,La0/mozilla-relengapi,mozilla-releng/services,mozilla-releng/services