Fix a missing close parenthesis in docstring

[Andrew-S-Rosen]

This is yet another super minor fix. Here, I have fixed a missing close parenthesis in a docstring with a ln().

I was just curious about the features in pyEQL and this caught my eye, so I had to fix it. 😅

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.73%. Comparing base (4d458ca) to head (94f2434).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #124   +/-   ##
=======================================
  Coverage   81.73%   81.73%           
=======================================
  Files           9        9           
  Lines        1429     1429           
  Branches      294      294           
=======================================
  Hits         1168     1168           
  Misses        221      221           
  Partials       40       40           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[rkingsbury]

Thanks @Andrew-S-Rosen , appreciate you taking the time to fix!