remove unused npm import

mod.ts

@@ -4,7 +4,6 @@ import {
 } from "https://deno.land/[email protected]/http/http_status.ts";
 import * as path from "https://deno.land/[email protected]/path/mod.ts";
 import * as cookie from "https://deno.land/[email protected]/http/cookie.ts";
-import prettyTime from "npm:pretty-time";
 
 type ListenOptions = {
   port: number;