Fixup return statement warning on module install

Hi,

Fresh to golang - but noticed when installing your goagain module it produces a warning (which is causing issues with my puppet provider). Warning is:

root@ops-foo:~# go get github.com/rcrowley/goagain     
# github.com/rcrowley/goagain
/usr/lib/go/src/pkg/github.com/rcrowley/goagain/goagain.go:23: function ends without a return statement