Add Arbitrary instance for NonEmpty Strings

[fthomas]

No description provided.

[fthomas]

This is not binary compatible with 0.8 and therefore needs to wait until 0.9.

[codecov]

Codecov Report

Merging #415 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #415      +/-   ##
==========================================
+ Coverage   95.76%   95.79%   +0.02%     
==========================================
  Files          46       46              
  Lines         590      594       +4     
  Branches       12       14       +2     
==========================================
+ Hits          565      569       +4     
  Misses         25       25

Impacted Files	Coverage Δ
...n/scala/eu/timepit/refined/scalacheck/string.scala	100% <100%> (ø)	⬆️

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[fommil]

you might want to do a .toString on the char to avoid an implicit. Wartremover and scalafix usually catch that.