(SERVER-2113) Update version to 5.2.0
(SERVER-2113) Update version to 5.2.0

This commit updates puppetserver's version to 5.2.0 in preparation for
release.

puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppet-server