docs: fix typo

[chuanchang]

Signed-off-by: Alex Jia [email protected]

Ⅰ. Describe what this PR did

as summary, this PR fixes some typo in documents.

Ⅱ. Does this pull request fix one issue?

fixes #1302

Ⅲ. Describe how you did it

using aspell checker

Ⅳ. Describe how to verify it

using spell tool to check

Ⅴ. Special notes for reviews

[pouchrobot]

Thanks for your contribution. 🍻 @chuanchang
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]

We found this is your first time to contribute to Pouch, @chuanchang
👏 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.

[allencloud]

LGTM unless you signed the CLA. Thanks a lot. @chuanchang

[codecov-io]

Codecov Report

Merging #1303 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1303   +/-   ##
=======================================
  Coverage   16.45%   16.45%           
=======================================
  Files         182      182           
  Lines       11285    11285           
=======================================
  Hits         1857     1857           
  Misses       9292     9292           
  Partials      136      136