Docs: Use link to tagged version for rule docs

[sudo-suhas]

This adds a utility function and uses the version present in package.json for generating the URL to tagged version of the rule documentation. I think this is good because the documentation will match the version the user has installed. This way, even if a rule is changed or removed in the future, the user can find the documentation with ease.

Note: This is very similar to the PR mysticatea/eslint-plugin-eslint-comments#11, but including the same description just to be through.

[codecov-io]

Codecov Report

Merging #104 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #104      +/-   ##
==========================================
+ Coverage   98.52%   98.54%   +0.02%     
==========================================
  Files          42       43       +1     
  Lines        1014     1030      +16     
==========================================
+ Hits          999     1015      +16     
  Misses         15       15

Impacted Files	Coverage Δ
lib/rules/no-deprecated-api.js	100% <100%> (ø)	⬆️
lib/rules/no-extraneous-import.js	91.66% <100%> (+0.75%)	⬆️
lib/rules/no-missing-require.js	100% <100%> (ø)	⬆️
lib/rules/no-missing-import.js	100% <100%> (ø)	⬆️
lib/rules/shebang.js	97.56% <100%> (+0.06%)	⬆️
lib/rules/exports-style.js	98.3% <100%> (+0.02%)	⬆️
lib/util/get-docs-url.js	100% <100%> (ø)
lib/rules/no-unpublished-import.js	100% <100%> (ø)	⬆️
lib/rules/no-unpublished-bin.js	92.85% <100%> (+0.26%)	⬆️
lib/rules/no-unpublished-require.js	100% <100%> (ø)	⬆️
... and 4 more

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[mysticatea]

LGTM, thank you!!