Fix issue #364: typo in StdTetExp::v_LocCollapsedToLocCoord calculation

Issue/feature addressed

Fixes #364 (closed) which identifies a problem in StdTetExp::v_LocCollapsedToLocCoord with eta[0] used instead of eta[1].

Proposed solution

Fixed the typo, and added unit test to ensure the mapping + inverse mapping give the identity.

Checklist

• Functions and classes, or changes to them, are documented.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).