Fix TypeScript types (#1)

The correct way to type `module.exports =`, is using the TypeScript
syntax `export =`. For CJS `export default` in TypeScript represents
`module.exports.default`.

Author: remcohaszing

index.d.ts

@@ -1 +1,3 @@
-export default function detach(buf: ArrayBuffer | ArrayBufferView): void;
+declare function detach(buf: ArrayBuffer | ArrayBufferView): void;
+
+export = detach;