When the [bug report] slider component is initialized, it still sends out input events, but in some cases, it is not practical

### Element UI version
2.9.1

### OS/Browsers version
macos10.15.3 / chrome 80.0.3987.149

### Vue version
2.6.10

### Reproduction Link
https://jsfiddle.net/kdouans2/

### Steps to reproduce
打开重现链接，接着打开控制台发现有两个输出"input change"

### What is Expected?
没有任何输出，也就是说初始化slider组件不要触发input或者change事件。

### What is actually happening?
有两个输出"input change"，可以发现初始化时就触发了两次。