Check MonadTests for Vector and List

[ceedubs]

This is surprising to me, so I may be missing something, but as far as I
can tell, we weren't running the MonadTests for Vector and List.

[johnynek]

OMG.

Maybe we should do a push to see what code is not covered by tests to see if we can more such examples.

[ceedubs]

Indeed the way that I discovered this was by noticing that tailRecM for Vector didn't have coverage.

[codecov-io]

Codecov Report

Merging #2214 into master will increase coverage by 0.2%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #2214     +/-   ##
=========================================
+ Coverage   94.83%   95.04%   +0.2%     
=========================================
  Files         333      333             
  Lines        5789     5789             
  Branches      211      211             
=========================================
+ Hits         5490     5502     +12     
+ Misses        299      287     -12

Impacted Files	Coverage Δ
core/src/main/scala/cats/instances/vector.scala	100% <0%> (+27.27%)	⬆️

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