AURORA-590: Release scripts branch and CHANGELOG urls are wrong in generated email template

Fixes urls in email templates to point to correct locations

Testing Done:
The CHANGELOG for the release is available at:
https://git-wip-us.apache.org/repos/asf?p=incubator-aurora.git&f=CHANGELOG&hb=0.5.0-rc1

The branch used to create the release candidate is:
https://git-wip-us.apache.org/repos/asf?p=incubator-aurora.git&hb=0.5.0-rc1

Bugs closed: AURORA-590

Reviewed at https://reviews.apache.org/r/23688/