Update the URL for GitHub Enterprise
Update the URL for GitHub Enterprise

It moved to a "real" hostname with a real certificate on the evening of
2017-05-11 as described in this announcement:

- https://sites.google.com/a/digital.cabinet-office.gov.uk/gds-internal-it/github-enterprise-change-5-30pm-6pm-11th-may-2017/githubdigitalcabinet-officegovuk

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf