Drop support for doctrine/inflector 2

Hi makers!

This is a tiny release that reverts aa change in v1.17.0. Specifically, this release removes support for doctrine/inflector 2.0. That may seem odd (and it is!) but allowing support made it likely that installing MakerBundle and then other libraries (like doctrine/orm) would fail. See #611 for the change and #610 for more information.

Happy making!