update to latest rust
update to latest rust

dtwood/piston-image,theotherphil/image,nwin/rust-image,huonw/image,twoodford/image,JaySon-Huang/image,bvssvni/image,hetzge/image,PistonDevelopers/image,lady-segfault/image,TyOverby/rust-image,PistonDevelopers/image,ruud-v-a/image,mbrubeck/image,tomaka/image