Do not build ruby in parallel.
Do not build ruby in parallel.

Fails when building on Ubuntu 15.04.

wcamarao/bosh-vsphere-cpi-release,nimbus-cloud/bosh-vsphere-cpi-release,rexxar-liang/bosh-vsphere-cpi-release,wcamarao/bosh-vsphere-cpi-release,wcamarao/bosh-vsphere-cpi-release,cloudfoundry-incubator/bosh-vsphere-cpi-release,rexxar-liang/bosh-vsphere-cpi-release,nimbus-cloud/bosh-vsphere-cpi-release,rexxar-liang/bosh-vsphere-cpi-release,cloudfoundry-incubator/bosh-vsphere-cpi-release,cloudfoundry-incubator/bosh-vsphere-cpi-release,nimbus-cloud/bosh-vsphere-cpi-release,cloudfoundry-incubator/bosh-vsphere-cpi-release,cloudfoundry-incubator/bosh-vsphere-cpi-release