[bug report] set the indicator to outside in the vertical direction of the riding lamp. There is a problem with the indicator position

### Element UI version
2.13.0

### OS/Browsers version
win10，chrome浏览器

### Vue version
2.6.7

### Reproduction Link
https://codepen.io/aol121/pen/PowaNBJ

### Steps to reproduce

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### What is Expected?
期望指示器在走马灯右外侧

### What is actually happening?
指示器在下方