Check Traverse laws for XorT

[ceedubs]

There was a typo before that caused the XorT tests to only check the
Foldable laws for the Traverse instance.

[codecov-io]

Current coverage is 82.99%

Merging #680 into master will increase coverage by +0.05% as of 18b0d8c

@@            master    #680   diff @@
======================================
  Files          162     162       
  Stmts         2217    2217       
  Branches        74      74       
  Methods          0       0       
======================================
+ Hit           1839    1840     +1
  Partial          0       0       
+ Missed         378     377     -1

Review entire Coverage Diff as of 18b0d8c

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[non]

👍

[adelbertc]

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