Fix incorrect tag size limit

[alexey-igrychev]

A tag name must be valid ASCII and may contain lowercase and uppercase letters, digits, underscores, periods and dashes. A tag name may not start with a period or a dash and may contain a maximum of 128 characters.

[google-cla]

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[alexey-igrychev]

@googlebot I signed it!

[codecov-commenter]

Codecov Report

Merging #760 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #760   +/-   ##
=======================================
  Coverage   79.02%   79.02%           
=======================================
  Files         102      102           
  Lines        4734     4734           
=======================================
  Hits         3741     3741           
  Misses        550      550           
  Partials      443      443           

Impacted Files	Coverage Δ
pkg/name/tag.go	100.00% <100.00%> (ø)

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[jonjohnsonjr]

Thanks!