use correct sha1 on light stemcells
use correct sha1 on light stemcells

[#134451441](https://www.pivotaltracker.com/story/show/134451441)

Signed-off-by: Chris Hajas <e8e414b713ceee89684f46616039fe9bed26bfcc@pivotal.io>

erjohnso/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release,erjohnso/bosh-google-cpi-release,erjohnso/bosh-google-cpi-release,erjohnso/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release,cloudfoundry-incubator/bosh-google-cpi-release,evandbrown/bosh-google-cpi-release