fix: properly join publicPath, basePath

[MoyuScript]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

When output.publicPath is not ends with /, the path of output will be incorrect.

Webpack configuration:

output: {
   publicPath: '/public/js'
 },

Wrong output:

{
  "index.js": "/public/jsindex.04565a72d083184c3c5a.js"
}

Correct output:

{
  "index.js": "/public/js/index.04565a72d083184c3c5a.js"
}

[shellscape]

Thanks for the PR. Looks like you have a few failing tests to address before we can accept it.

[shellscape]