Update EASE in edx-platform requirements

Currently, the EASE repository installs the NLTK corpus in its `setup.py`.  We're already installing NLTK using the Ansible scripts, so this wastes disk space.

This change removes the NLTK corpus from the EASE repository.  It also includes a minor change to error message logging.

Full changes:
https://github.com/edx/ease/compare/6eee938f98777367b414217c09a8dce05efc2d7f...ea5770eaba4ce129cb5db8a41662435649ba6d4c

Note that this change will NOT affect ORA1 installations, since those use the version of EASE installed for the `ora` user.  This change will only affect ORA2 AI grading.

@singingwolfboy