change refute => assert for ruby 1.8.7
change refute => assert for ruby 1.8.7

bquorning/fakefs,anthonyryan1/fakefs,vhl/fakefs,defunkt/fakefs,deployable/fakefs,pivotal-cf-experimental/fakefs,bf4/fakefs,fakefs/fakefs,onehub/fakefs,1234-/fakefs,eventualbuddha/fakefs,marxarelli/fakefs,dekz/fakefs