Use Check.name in repr

[JacobHayes]

Previously Check.name could be set but was unused and the __repr__ fell back to the fn name, which isn't particularly useful for lambdas. This change uses the name argument in the repr, but keeps the same fallback, which has moved to __init__.

[codecov-commenter]

Codecov Report

Merging #265 into master will increase coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #265      +/-   ##
==========================================
+ Coverage   96.62%   96.78%   +0.15%     
==========================================
  Files          15       15              
  Lines        1332     1491     +159     
==========================================
+ Hits         1287     1443     +156     
- Misses         45       48       +3     

Impacted Files	Coverage Δ
pandera/checks.py	98.59% <100.00%> (+0.20%)	⬆️
pandera/decorators.py	90.80% <0.00%> (-1.74%)	⬇️
pandera/errors.py	100.00% <0.00%> (ø)
pandera/schema_components.py	98.97% <0.00%> (+0.56%)	⬆️
pandera/hypotheses.py	94.11% <0.00%> (+1.66%)	⬆️

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