Make CI use ES 2.4
Make CI use ES 2.4

Licence finder which is the only app on ES 1.7 will pass all tests on ES 2.4
and does not specify a version in it's Jenkinsfile.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet