Fix npm update command for snapshot summary

[kdnakt]

Summary

The snapshot summary told me to use npm test -u but it didn't work and needs special option -- to update snapshot.
This fix tells the correct command to update snapshot for npm.

Test plan

With npm test, I got this summary.

With yarn test.

[codecov-io]

Codecov Report

Merging #5376 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #5376      +/-   ##
==========================================
- Coverage   61.33%   61.32%   -0.01%     
==========================================
  Files         205      205              
  Lines        6924     6925       +1     
  Branches        3        4       +1     
==========================================
  Hits         4247     4247              
- Misses       2676     2677       +1     
  Partials        1        1

Impacted Files	Coverage Δ
...ackages/jest-cli/src/reporters/summary_reporter.js	14.75% <0%> (-0.25%)	⬇️

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[SimenB]

Thanks!

[cpojer]

This is an awesome tiny fix. Thanks for sending a PR.

[github-actions]

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