path resolution fails on Windows

[zvmsbackend]

On windows, the racks compiler produces javascript code like

import * as $rjs_core from '..\runtime\core.js';import * as M0 from "..\collects\racket\private\stream-cons.rkt.js";...

which is invalid in js.

This was caused by the direct use of format on path object in procedure racketscript-compiler/compiler/assembler.rkt/assemble-requires*. I think simply adding a string-replace would solve the problem.

However, this is yet to be solved till now. A similar issue (#249) has been posted two years ago, but closed unintentionaly.