Add protocol to stdError (#277)

* Add protocol property to error properties test

* Add protocol to stdError object

Adds the protocol to the stdError object got uses for all its errors.
Closes #249.

index.js

@@ -334,7 +334,8 @@ function stdError(error, opts) {
 		host: opts.host,
 		hostname: opts.hostname,
 		method: opts.method,
-		path: opts.path
+		path: opts.path,
+		protocol: opts.protocol
 	});
 }
 

test/error.js

@@ -27,6 +27,7 @@ test('properties', async t => {
 		t.is(err.message, 'Response code 404 (Not Found)');
 		t.is(err.host, `${s.host}:${s.port}`);
 		t.is(err.method, 'GET');
+		t.is(err.protocol, 'http:');
 	}
 });