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fix kubectl get cronjob lose age info

**What this PR does / why we need it**:
relate with #20941
befere output:
```
NAME      SCHEDULE      SUSPEND   ACTIVE    LAST SCHEDULE   AGE
pi        0/5 * * * ?   False     1         Thu, 14 Sep 2017 20:10:00 +0800
```
now output:
```
admindeMacBook-Pro-2:kubectl admin$ ./kubectl get cronjob
NAME      SCHEDULE      SUSPEND   ACTIVE    LAST SCHEDULE   AGE
pi        0/5 * * * ?   False     1         3m              4m
```

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:
thanks
**Release note**:

```release-note
NONE
```