[Bug Report] Steps component with align-center will be shorter then width given / parent element

### Element UI version
0.1.0

### OS/Browsers version
Chrome 81 on Windows 10

### Vue version
2.6.1

### Reproduction Link
https://jsfiddle.net/mep5o8yx/5/

### Steps to reproduce
Use the steps component with align-center and a width / parent div with width.

### What is Expected?
The steps component width will be extended to the entire width.
Like the same component without align-center - where its working correctly.

### What is actually happening?
The steps component label/ title will end before the div width is filled.
Making it impossible to stick to right / left of page.