Bump version of paas-billing to v0.9.0
Bump version of paas-billing to v0.9.0

We want to deploy the pricing simulation feature implemented
in alphagov/paas-billing#11

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf