SERVER-27107, after branching 3.6, we should bump the version in the following places:
For master branch:
- update multiversion to download 3.6: https://github.com/mongodb/mongo/blob/r3.6.0-rc0/etc/evergreen.yml#L975
- update https://github.com/mongodb/mongo/blob/r3.6.0-rc0/src/mongo/shell/servers.js#L126
- bump verify_versions_test.js from 3.6 to 3.7
- remove any multiversion tests that are specifically testing 3.4 <~~> 3.6 upgrade/downgrade scenarios.