Bump nix version to v0.4.2
Bump nix version to v0.4.2

dwrensha/mio,murarth/mio,carllerche/mio,mneumann/mio,mneumann/mio,carllerche/mio,danburkert/mio,arthurprs/mio,rrichardson/mio,asomers/mio,asomers/mio,fuchsia-mirror/third_party-mio,fuchsia-mirror/third_party-mio