I wouldn't worry that much about it, the differences between Django 1.11 and Django 2.0 aren't major ones with the exception of dropping support for Python 2.x and the new simplified URL routing syntax.
Django 1.11 is a LTS (Long Term Support) release so it will have security upgrades until 2020, so you are safe sticking with it.
However I'd go ahead with 1.11 and transition to 2.0 to learn how Django handles deprecation and how to upgrade a codebase, both very useful skills as Django has a steady release process and it's often easier to track Django than to do a multi-version migration.
