feat: support not keyword

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Support not keyword

Breaking Changes

No

Additional Info

Some messages can be invalid need more tests

For example:

{ "not": { "minimum": 3 } }

Should output should not be < 3 or any non-number

[codecov]

Codecov Report

Merging #53 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #53      +/-   ##
==========================================
+ Coverage   98.49%   98.51%   +0.01%     
==========================================
  Files           4        4              
  Lines         466      472       +6     
  Branches      211      215       +4     
==========================================
+ Hits          459      465       +6     
  Misses          7        7

Impacted Files	Coverage Δ
src/ValidationError.js	98.27% <100%> (+0.02%)	⬆️

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