[bug report] when the input component is password and: Disabled = 'true', the element disable status (gray) is invalid

### Element UI version
2.13.0

### OS/Browsers version
win10

### Vue version
2.6.9

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

### Steps to reproduce
当input组件为password，:disabled='true'的时候，前后元素包括password元素字体颜色不为灰色

### What is Expected?
元素变为禁用状态（灰色）

### What is actually happening?
元素状态未改变