update(package.json): os-indpendent copy

[G0maa]

• files filed in package.json by itself doesn't copy files to dist
• This has been an issue (in TS) for a while see
• fixes: [bug]: cp cmd in build script not working for windows keploy#372
• Edit: I took a look at the other PR, it may have a better solution as it doesn't add an extra dependency.

[developer-diganta]

@re-Tick Can you please review this?

[re-Tick]

I think the other approach is better since adding a package for this would not be a good option.