[Bug Report] el-input regression when using v-model.number

### Element UI version
^2.5.0

### OS/Browsers version
Windows/Firefox 70.0.1, Chrome 78.0.3904.70

### Vue version
2.6.10

### Reproduction Link
https://codepen.io/skolos/pen/bGGKKdX

### Steps to reproduce
1. Try typing into input box: 1.1
It will not allow typing decimal period and will end up typing 11

2. If change element-ui version to 2.4.11 (i.e. using "//unpkg.com/element-ui@2.4.11/lib/index.js" link in HTML part), there is no issue (i.e. will end up typing 1.1)

3. If change element-ui version to anything from 2.5.0 and up, the issue is present.

### What is Expected?
Will be able to type 1.1

### What is actually happening?
Cannot type 1.1, instead getting 11.

Looks like the regression is caused by this PR: https://github.com/ElemeFE/element/pull/13471