add test to ensure gzip works in stream mode

package.json

@@ -62,6 +62,7 @@
     "ava": "^0.14.0",
     "coveralls": "^2.11.4",
     "get-port": "^2.0.0",
+    "get-stream": "^1.1.0",
     "into-stream": "^2.0.0",
     "nyc": "^6.0.0",
     "pem": "^1.4.4",

test/gzip.js

@@ -1,5 +1,6 @@
 import zlib from 'zlib';
 import test from 'ava';
+import getStream from 'get-stream';
 import got from '../';
 import {createServer} from './helpers/server';
 
@@ -37,6 +38,10 @@ test('decompress content', async t => {
 	t.is((await got(s.url)).body, testContent);
 });
 
+test('decompress content - stream', async t => {
+	t.is(await getStream(got.stream(s.url)), testContent);
+});
+
 test('handles gzip error', async t => {
 	try {
 		await got(`${s.url}/corrupted`);