fix(module:cron-expression): clear ul & li default style

[OriginRing]

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/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?

[ ] 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?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #7715 (bd92e2d) into master (3a638af) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7715   +/-   ##
=======================================
  Coverage   92.02%   92.02%           
=======================================
  Files         502      502           
  Lines       16762    16762           
  Branches     2638     2638           
=======================================
  Hits        15426    15426           
  Misses       1069     1069           
  Partials      267      267           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[simplejason]

LGTM