remove undefined code in errors

index.js

@@ -326,9 +326,12 @@ helpers.forEach(function (el) {
 });
 
 function stdError(error, opts) {
+	if (error.code !== undefined) {
+		this.code = error.code;
+	}
+
 	objectAssign(this, {
 		message: error.message,
-		code: error.code,
 		host: opts.host,
 		hostname: opts.hostname,
 		method: opts.method,

test/error.js

@@ -23,6 +23,7 @@ test('properties', async t => {
 		t.ok(err);
 		t.ok(err.response);
 		t.ok(!err.propertyIsEnumerable('response'));
+		t.ok(!err.hasOwnProperty('code'));
 		t.is(err.message, 'Response code 404 (Not Found)');
 		t.is(err.host, `${s.host}:${s.port}`);
 		t.is(err.method, 'GET');