Use rustup to handle installation for travis
Use rustup to handle installation for travis

rustup now installs both the latest rust nightly and cargo,
so we no longer need to manually manage the installation process
for cargo or rust.

tempbottle/piston,PistonDevelopers/piston,mitchmindtree/piston,getynge/piston,bvssvni/piston,caldwell/piston,placrosse/piston,KevinFrans3/piston,bvssvni/piston,axelmagn/piston,PistonDevelopers/piston,Potpourri/piston,oldmanmike/piston