Allow regex to handle previos buildpack-cached zip file.
Allow regex to handle previos buildpack-cached zip file.

The prior buildpack-cached zip file will not have a stack name in it, because we only just started putting one in. This loosens the regex to allow for that.

[#157745313]

Signed-off-by: Tyler Phelan <5713437ebd3bcae14564c2baaa7816b900ed174c@pivotal.io>

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