Increase timeout of web unit tests (microsoft#156894)

* Windows: some Firefox web tests are timing out randomly (microsoft#155760)

See if this is a fundamental issue or really Firefox is slower.

* mention issue

Author: bpasero

test/unit/browser/renderer.html

@@ -33,7 +33,7 @@
 
 		mocha.setup({
 			ui: 'tdd',
-			timeout: 5000
+			timeout: 30000 // https://github.com/microsoft/vscode/issues/155760
 		});
 	</script>