fix version spelling

[seriousben]

Just noticed this spelling error while looking at the source.

[googlebot]

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[seriousben]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

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[codecov-io]

Codecov Report

Merging #1181 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1181   +/-   ##
=======================================
  Coverage   54.23%   54.23%           
=======================================
  Files          42       42           
  Lines        4270     4270           
=======================================
  Hits         2316     2316           
  Misses       1695     1695           
  Partials      259      259           

Impacted Files	Coverage Δ
protoc-gen-swagger/main.go	26.60% <ø> (ø)

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[achew22]

Thanks so much for contributing to the project!