fix(module:date-picker): fix code comment

[cxb1021]

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?
fix code comment in date picker component

[ ] 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]

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[codecov]

Codecov Report

Merging #7991 (9d72baa) into master (198644a) will increase coverage by 91.81%.
The diff coverage is n/a.

❗ Current head 9d72baa differs from pull request most recent head ed98d7b. Consider uploading reports for the commit ed98d7b to get more accurate results

@@             Coverage Diff             @@
##           master    #7991       +/-   ##
===========================================
+ Coverage        0   91.81%   +91.81%     
===========================================
  Files           0      509      +509     
  Lines           0    17452    +17452     
  Branches        0     2774     +2774     
===========================================
+ Hits            0    16024    +16024     
- Misses          0     1135     +1135     
- Partials        0      293      +293     

Impacted Files	Coverage Δ
components/date-picker/date-picker.component.ts	95.25% <ø> (ø)

... and 508 files with indirect coverage changes