[Bug Report] TimePicker format issue.

### Element UI version
2.14.1

### OS/Browsers version
Google chrome Version 87.0.4280.88 (Official Build) (64-bit)

### Vue version
2.6.12

### Reproduction Link
https://codepen.io/pen/?&prefill_data_id=1d3c4f76-d95e-4e86-a7eb-e5042dc3de92

### Steps to reproduce
1. component->timePicker
2. use Arbitrary time range
3. value-format: "HH:mm"
4. initialize the binding value with an Array: [new Date(), new Date()].

### What is Expected?
fix it.

### What is actually happening?
Time picker format issue, there's an issue when i use Arbitrary time range, value-format is "HH:mm", and i bind default value for the component which is an array like [new Date(), new Date()], and i log the array out put is like: 23:59:00 GMT 0805 (China Standard Time)