fix: explicitly import URL so that .d.ts file is correctly generated (#1992)

* fix: explicitly import URL so that .d.ts file is correctly generated

* add URL import in file as well

Author: ddelgrosso1

src/bucket.ts

@@ -64,6 +64,7 @@ import {
 } from './signer';
 import {Readable} from 'stream';
 import {CRC32CValidatorGenerator} from './crc32c';
+import {URL} from 'url';
 
 interface SourceObject {
   name: string;

src/file.ts

@@ -68,6 +68,7 @@ import {
 } from './util';
 import {CRC32CValidatorGenerator} from './crc32c';
 import {HashStreamValidator} from './hash-stream-validator';
+import {URL} from 'url';
 
 import retry = require('async-retry');