docs: fix typo

[renlulu]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[pouchrobot]

Thanks for your contribution. 🍻 @renlulu
While we thought PR TITLE could be more specific, longer than 20 chars.
Please edit this PR title instead of opening a new one.
More details, please refer to https://github.com/alibaba/pouch/blob/master/CONTRIBUTING.md

[pouchrobot]

@renlulu Thanks for your contribution. 🍻
Please sign off in each of your commits.

[pouchrobot]

We found this is your first time to contribute to Pouch, @renlulu
👏 We really appreciate it.
Just remind that you have read the contribution guide: https://github.com/alibaba/pouch/blob/master/CONTRIBUTING.md
If you didn't, you should do that first. If done, welcome again and please enjoy hacking! 🍻

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #904 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #904   +/-   ##
=====================================
  Coverage      14%    14%           
=====================================
  Files         119    119           
  Lines        7477   7477           
=====================================
  Hits         1047   1047           
  Misses       6341   6341           
  Partials       89     89

Impacted Files	Coverage Δ
cli/top.go	0% <ø> (ø)	⬆️

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[HusterWan]

@renlulu very appreciative of your work， please sign the CLA, thanks a lot

[allencloud]

LGTM