Update response.js (#1162)

Allow Response.clone() to persist the high water mark

src/response.js

@@ -95,7 +95,8 @@ export default class Response extends Body {
 			headers: this.headers,
 			ok: this.ok,
 			redirected: this.redirected,
-			size: this.size
+			size: this.size,
+			highWaterMark: this.highWaterMark
 		});
 	}
 

test/response.js

@@ -122,7 +122,8 @@ describe('Response', () => {
 			},
 			url: base,
 			status: 346,
-			statusText: 'production'
+			statusText: 'production',
+			highWaterMark: 789
 		});
 		const cl = res.clone();
 		expect(cl.headers.get('a')).to.equal('1');
@@ -130,6 +131,7 @@ describe('Response', () => {
 		expect(cl.url).to.equal(base);
 		expect(cl.status).to.equal(346);
 		expect(cl.statusText).to.equal('production');
+		expect(cl.highWaterMark).to.equal(789)
 		expect(cl.ok).to.be.false;
 		// Clone body shouldn't be the same body
 		expect(cl.body).to.not.equal(body);