element-ui to element-plus index.css modification

[LandaHao]

Describe the bug
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originjs/vue2-element-touzi-admin@8cddf35
To Reproduce
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NA
Expected behavior
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import('element-ui/lib/theme-chalk/index.css') should be changed to
import('element-plus/theme-chalk/index.css')
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Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]
  element-plus 2.2.17

Additional context
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