Feat/trappe ua combrule

[justinGilmer]

PR Summary:

After the addition of the combining_rule forcefield XML metadata, we added the geometric mixing rule to oplsaa.xml, but neglected to include that information for our TraPPE xml.

This includes the Lorentz-Berethlot mixing rule as metadata as well as bumping the version number for the trappe-ua.xml file.

A minor spelling mistake was also fixed.

PR Checklist

---

• [x] Includes appropriate unit test(s)
• [x] Appropriate docstring(s) are added/updated
• [x] Code is (approximately) PEP8 compliant
• [ ] Issue(s) raised/addressed?

[daico007]

Do we also want a CHANGLOG.md for Trappe XML

[codecov[bot]]

Codecov Report

Merging #452 (0aa062b) into master (78dbdaf) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #452   +/-   ##
=======================================
  Coverage   73.88%   73.88%           
=======================================
  Files          17       17           
  Lines        1842     1842           
=======================================
  Hits         1361     1361           
  Misses        481      481           

[justinGilmer]

We absolutely do, I forgot about that. Will add that in a second.