Use github.com/srvc/fail v4.1.1

[qnighy]

Upgrade github.com/srvc/fail for:

• Better go modules integration.
• Newest features from srvc/fail.

[qnighy]

Note, this is technically a breaking change because we use fail.Error in our interface.

[codecov-io]

Codecov Report

Merging #21 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #21   +/-   ##
=======================================
  Coverage   56.48%   56.48%           
=======================================
  Files           5        5           
  Lines         108      108           
=======================================
  Hits           61       61           
  Misses         46       46           
  Partials        1        1

Impacted Files	Coverage Δ
unary_server_error_handlers.go	91.66% <ø> (ø)	⬆️
stream_server_error_handlers.go	0% <ø> (ø)	⬆️
handlers.go	90.24% <ø> (ø)	⬆️

---

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