fix: windows output path

[huozhi]

The path could be relative but sort of absolute, so we always need to replace the leading cwd path, and also replace the sep to /

Before

Exports  File                                                                                     Size
.        ../D:\a\bunchee\bunchee\test\integration\dev-prod-convention\dist/index.development.mjs  48 B
         ../D:\a\bunchee\bunchee\test\integration\dev-prod-convention\dist/index.development.js   53 B
         ../D:\a\bunchee\bunchee\test\integration\dev-prod-convention\dist/index.production.mjs   47 B

After

Exports  File                                                                                     Size
.        dist/index.development.mjs  48 B
         dist/index.development.js   53 B
         dist/index.production.mjs   47 B