[bug report] el-progress content is not change,but value change

Element UI version
2.13.0

OS/Browsers version
Version 80.0.3987.116

Vue version
2.6.10

Reproduction Link
https://codepen.io/usualminds/pen/jOPMBPg

Steps to reproduce
-- click start button
-- el-progress cotent not change ,but value change;

What is Expected?
el-progress cotent and value change at a time;
What is actually happening?
el-progress cotent not change ,but value change;