cmd/jv: flag parsing and usage fixes

[scop]

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.01% :warning:

Comparison is base (bbc9f89) 89.21% compared to head (b9a55db) 89.21%. Report is 4 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #127      +/-   ##
==========================================
- Coverage   89.21%   89.21%   -0.01%     
==========================================
  Files          10       10              
  Lines        2652     2651       -1     
==========================================
- Hits         2366     2365       -1     
  Misses        237      237              
  Partials       49       49              

see 1 file with indirect coverage changes

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[scop]

Looks like this is half obsolete as of 6.0.1, reworked remainders in https://github.com/santhosh-tekuri/jsonschema/pull/177, closing here.