[Bug Report] Loss of precision when stepStrictly is true and step as 0.00001 in el-input-number

### Element UI version
2.13.1

### OS/Browsers version
window 10/chrome 81.0.4044.122

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/huangchen1031/pen/vYNZyrw

### Steps to reproduce

when num is 2

### What is Expected?
return 2

### What is actually happening?
the component return 2.0000000000000004