[Bug Report] el-input-number will trigger the validator when input some value

### Element UI version
2.13.2

### OS/Browsers version
Windows 10 / Chromium 80.0.3987.163

### Vue version
2.6.12

### Reproduction Link
https://codepen.io/konp/pen/dyMJEvx

### Steps to reproduce
1. click the input
2. enter "1"

### What is Expected?
the async-validator not be triggered

### What is actually happening?
the async-validator be triggered, do again and the validator gone