Fixing the TypeScript type for the init function

[Pauan]

When generating the init function for the web target, the TypeScript type was outdated, so this PR fixes that:

export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;

export interface InitOutput {
  readonly memory: WebAssembly.Memory;
  readonly main_js: () => void;
  readonly __wbindgen_malloc: (a: number) => number;
  readonly __wbindgen_realloc: (a: number, b: number, c: number) => number;
  readonly __wbindgen_export_2: WebAssembly.Table;
  readonly __wbindgen_free: (a: number, b: number) => void;
  readonly __wbindgen_exn_store: (a: number) => void;
  readonly __wbindgen_start: () => void;
}

/**
* If `module_or_path` is {RequestInfo} or {URL}, makes a request and
* for everything else, calls `WebAssembly.instantiate` directly.
*
* @param {InitInput | Promise<InitInput>} module_or_path
*
* @returns {Promise<InitOutput>}
*/
export default function init (module_or_path?: InitInput | Promise<InitInput>): Promise<InitOutput>;

[alexcrichton]

Looks like a rustfmt is needed but otherwise r=me!