Bump minimum supported to Julia 1.6

[odow]

Julia 1.0 is untested, and in fact will not work because this package contains a lot of calls like isnothing which are not defined in 1.0.

The simplest solution is just to restrict Pavito to 1.6 and later. It's going to be the new LTS anyway.

[codecov]

Codecov Report

Merging #47 (72f5a35) into master (48303fe) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #47   +/-   ##
=======================================
  Coverage   85.76%   85.76%           
=======================================
  Files           4        4           
  Lines         583      583           
=======================================
  Hits          500      500           
  Misses         83       83           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 48303fe...72f5a35. Read the comment docs.