[bug report] autocomplete does not work properly

### Element UI version
2.13.1

### OS/Browsers version
mac/Google Chrome80.0.3987.163

### Vue version
2.6.11

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

### Steps to reproduce
1.将官网上的demo中 输入文字 离开
2.autocomplete的离开触发handleChange事件 这里的event应该是el-input的value值 没有target属性 这样会报错
handleChange: function handleChange(event) {
this.$emit('change', event.target.value);
},

Error in v-on handler: "TypeError: Cannot read property 'value' of undefined"

found in

at packages/input/src/input.vue
at packages/autocomplete/src/autocomplete.vue

### What is Expected?
1.不报错
2.正常显示

### What is actually happening?
1.handleChange中的event是value 不是event对象 会报错
2.element大佬应该不会犯这种低级错误 感觉是哪个实习生改的吧 这么重要的项目希望大佬们重视下呀