Fetch JS snippet (#1343)

* Add test for fetch snippet

* Add fetch snippet

* Fix jQuery doc comment

packages/insomnia-httpsnippet/test/fixtures/output/javascript/fetch/https.js

@@ -0,0 +1,9 @@
+const fetchOptions = {
+  mode: 'cors',
+  method: 'GET',
+  headers: {},
+};
+
+fetch('https://mockbin.com/har', fetchOptions)
+  .then(response => response.json())
+  .then(data => console.log(data));