Remove rubygem-mirror value from build-binary task
Remove rubygem-mirror value from build-binary task

[#128344211]

Signed-off-by: Jacques Chester <8f1e729cbc4d489c19883827c4c21d9fbbde0732@pivotal.io>

orange-cloudfoundry/buildpacks-ci,orange-cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,orange-cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci