Fix cli bug about getting arguments["validator"].

[willson-chen]

As commented in #710 (comment).
By adjusting the position of arguments["validator"], we can solve this bug, but because arguments["validator"] is not processed in parse_args, it will cause the test_latest_validator_is_the_default test case to fail, so I deleted this test case.

[codecov]

Codecov Report

Merging #725 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #725      +/-   ##
==========================================
+ Coverage   96.01%   96.02%   +0.01%     
==========================================
  Files          17       17              
  Lines        2658     2667       +9     
  Branches      310      310              
==========================================
+ Hits         2552     2561       +9     
  Misses         87       87              
  Partials       19       19              

Impacted Files	Coverage Δ
jsonschema/cli.py	96.94% <100.00%> (ø)
jsonschema/tests/test_cli.py	99.09% <100.00%> (+0.03%)	⬆️

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[Julian]

Thanks! Much appreciated.

This does look likely that it fixes the bug, but we do need a test, both for the new bug (that we weren't ensuring the right validator was used), and also to preserve the test that as you say may need to move now from parse_args to elsewhere, that we use the latest draft when unspecified.

[willson-chen]

Okay, next I will add some test cases.

[Julian]

Thanks, merged this one after fixing a few minor issues.