fix(module:transfer): fix transfer nzTargetKeys property

[Ricbet]

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?

[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?

Issue Number: #4641 #4360 #4210

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

This preview will be available after the TravisCI is passed.

[codecov]

Codecov Report

Merging #4670 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #4670      +/-   ##
=========================================
- Coverage   93.21%   93.2%   -0.02%     
=========================================
  Files         505     505              
  Lines       12742   12752      +10     
  Branches     1955    1957       +2     
=========================================
+ Hits        11877   11885       +8     
- Misses        455     456       +1     
- Partials      410     411       +1

Impacted Files	Coverage Δ
components/transfer/nz-transfer.component.ts	98.3% <100%> (+0.15%)	⬆️
components/typography/nz-typography.component.ts	98.23% <0%> (-0.89%)	⬇️
components/time-picker/time-holder.ts	97.31% <0%> (-0.68%)	⬇️

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