Fix method call

Can you please tag a new minor 2.1.* release after merging this PR? With this, the jackalope builds should be fixed (at least the non-lowest jobs)
ah that is why that worked locally but not on travis :-/ just did 2.1.2
hm, does that mean whenever we add/improve a test, we should tag a release? hm, not easy, having a separate test suite...