Drop Compat / Julia v0.6 Support

[ccoffrin]

Prepping for next release.

[codecov]

Codecov Report

Merging #436 into master will increase coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #436      +/-   ##
==========================================
+ Coverage   89.15%   89.29%   +0.14%     
==========================================
  Files           4        4              
  Lines        1272     1270       -2     
==========================================
  Hits         1134     1134              
+ Misses        138      136       -2     

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[chriscoey]

Thanks!