fix: direction error of QRCode

[Eve-Sama]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd-mobile/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?
修复了官网二维码介绍的方向错误

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

官网二维码的方向错位了, 之前是向上的popover, 会被导航栏遮挡.

Issue Number: N/A

What is the new behavior?

popover向下, 不会遮挡, 与react那边保持一致.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #739 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #739   +/-   ##
=======================================
  Coverage   87.16%   87.16%           
=======================================
  Files         164      164           
  Lines        6748     6748           
  Branches     1104     1104           
=======================================
  Hits         5882     5882           
  Misses        421      421           
  Partials      445      445           

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