add minified js files to the npm package

[njzjz]

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Issue Checklist

• I am using NexT version 8.0 or later.
• I have already read the relevant documents of Hexo and NexT.
• I have already searched for current issues, which does not help me.

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Expected behavior

Add minified js files to the npm package, so we can use the minified files from unpkg. Currently, only jsdelivr and cdnjs (and their mirrors) supports minified files.

Maybe we can execute webpack before npm publish? It should be devDependencies.