Bump sockjs-go from 2.0.1 to 2.1.0

[shu-mutou]

Latest release v2.0.1 uses CDN that have gone.

Closes #5064

[maciaszczykm]

/lgtm

[floreks]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floreks, maciaszczykm, shu-mutou

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[codecov]

Codecov Report

Merging #5073 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5073   +/-   ##
=======================================
  Coverage   45.48%   45.48%           
=======================================
  Files         214      214           
  Lines       10073    10073           
  Branches      100      100           
=======================================
  Hits         4582     4582           
  Misses       5225     5225           
  Partials      266      266           

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