[bug report] Using Loading.service Creating a global loading will close all message prompt messages when it is closed

### Element UI version
2.13.0

### OS/Browsers version
win10/chrome

### Vue version
2.6.11

### Reproduction Link
https://github.com/ElemeFE/element/issues

### Steps to reproduce
使用Loading.service创建全局loading 在使用loading.close时，会关闭所有message提示消息

### What is Expected?
loading只关闭自己，不影响其他详细或者弹窗

### What is actually happening?
使用Loading.service创建全局loading 在使用loading.close时，会关闭所有message提示消息