chore: upgrade eslint to 6.0

[afc163]

🤔 This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (upgrade deps)

👻 What's the background?

💡 Solution

📝 Changelog

Language	Changelog
🇺🇸 English
🇨🇳 Chinese

☑️ Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

[netlify]

Deploy preview for ant-design ready!

Built with commit 13deeb2

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[buildsize]

File name	Previous Size	New Size	Change
package-lock.json	834.28 KB	841.96 KB	7.68 KB (1%)

[codecov]

Codecov Report

Merging #17236 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17236      +/-   ##
==========================================
- Coverage   95.95%   95.93%   -0.03%     
==========================================
  Files         263      263              
  Lines        7351     7351              
  Branches     2055     2055              
==========================================
- Hits         7054     7052       -2     
- Misses        295      297       +2     
  Partials        2        2

Impacted Files	Coverage Δ
components/back-top/index.tsx	88.88% <0%> (-3.18%)	⬇️

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