Update travis to use 1.0.0-beta.4 and do not allow failures on beta.
Update travis to use 1.0.0-beta.4 and do not allow failures on beta.

The code should work with rust beta and rust nightly.

birkenfeld/racer,dleslie/racer,kbknapp/racer,BonsaiDen/racer,drewet/racer,syohex/racer,sthapaun/racer,syhkiller/racer,bluss/racer,syohex/racer,asantopietro/racer,andelf/racer,rranelli/racer,ifraixedes/racer,pmarcelll/racer,ane/racer,MattWis/racer,racer-rust/racer,alkama/racer,ane/racer,ajroetker/racer,hotpxl/racer,phildawes/racer,BonsaiDen/racer,bluss/racer,sthapaun/racer,syhkiller/racer,asantopietro/racer,drewet/racer,jaxx/racer,rranelli/racer,ifraixedes/racer,MattWis/racer,sliz1/racer,ajroetker/racer,Wilfred/racer,kbknapp/racer