not support windows path

[HerrCai0907]

// assembly/index.ts
import {a} from "../other/test"
export function add(a: i32, b: i32): i32 {
  return a + b;
}

// other/test.ts
export const a:i32 = 2

npx asc ./assembly/index.ts works
npx asc .\assembly\index.ts does not work

ERROR TS6054: File '/assembly/other/test.ts' not found.

import {a} from "../other/test"
~~~~~~~~~~~~~~~
in /assembly//index.ts(2,17)

FAILURE 1 parse error(s)