Update CI.yml to use LTS

[ViralBShah]

CI was failing for Julia 1.0. Bumping to 1.6 LTS.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 23.83%. Comparing base (343430a) to head (f12618e).
Report is 16 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #584      +/-   ##
==========================================
+ Coverage   22.92%   23.83%   +0.90%     
==========================================
  Files           4        4              
  Lines         362      365       +3     
==========================================
+ Hits           83       87       +4     
+ Misses        279      278       -1     

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