el-select option is not able to popup on top when el-select is in page foot

[yinjs]

Issue Type:

• [x] Bug
• [ ] Feature
• [ ] Help

Version & Environment:

0.7.2

Description: el-select option is not able to popup on top when el-select is in page foot.

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Footer [ el-select ] -------------------|----options--|---------------- .......................| not visible | .......................|...................| .......................|...................|

[unix]

this is a issue that needs to be improved, these components may need to be changed. i'll rewrite them in next feature version.