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

carllerche/mio,yangxingpping/mio,carllerche/mio,greensnark/mio,luca-barbieri/mio,mneumann/mio,danburkert/mio,mneumann/mio,rryan/mio,alexcrichton/mio,zslayton/mio,fhartwig/mio,arthurprs/mio,echochamber/mio,murarth/mio,dwrensha/mio,mlalic/mio,geofft/mio,asomers/mio,asomers/mio,fuchsia-mirror/third_party-mio,fuchsia-mirror/third_party-mio,marjakm/mio,frewsxcv/mio,rrichardson/mio,tailhook/mio