Inverting module export locations for multi-module publishing

[scalvert]

Fix for #142

[rwjblue]

Note for others, this fixes the type issues that folks still using ember-test-waiters as their import path were hitting. This does not fix any TS issues when attempting to use @ember/test-waiters (there really isn't anything we can do about that issue until we release the actual @ember/test-waiters package).