Point codegen at git, not the released verison
Point codegen at git, not the released verison

It currently relies on breaking changes coming in Diesel 0.5.0, which
makes the current git version unuseable.

mcasper/diesel,sgrif/diesel,SoftwareWarlock/diesel,SoftwareWarlock/diesel,diesel-rs/diesel,diesel-rs/diesel,sgrif/diesel,mcasper/diesel,tohou/diesel,cascalheira/diesel,cascalheira/diesel,tohou/diesel