Update docs/config/README.zh-CN.md

[zhangyu1818]

react-helmet名字错了

Checklist

• npm test passes
• tests are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

• any feature?
• close https://github.com/umijs/umi/ISSUE_URL

[codecov]

Codecov Report

Merging #5083 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5083   +/-   ##
=======================================
  Coverage   82.84%   82.84%           
=======================================
  Files         153      153           
  Lines        3381     3381           
  Branches      908      906    -2     
=======================================
  Hits         2801     2801           
- Misses        572      573    +1     
+ Partials        8        7    -1     

Impacted Files	Coverage Δ
packages/core/src/Config/Config.ts	61.78% <0.00%> (ø)

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