added extra argument to stub method

[andersgjetting]

added extra argument to stub method as some AWS sdk methods take more than 2 arguments e.g waitFor(state, params = {}, callback)

[rclark]

Thanks for this contribution! Could you please add a test that confirms that the functionality works as intended? As an example, you could build a test similar to this one, but stub waitFor and use 3 args:

mock-aws-sdk-js/test/index.test.js

Lines 31 to 49 in 041b5d5

	test('[useCallback] use replacement function', function(assert) {
	var getObject = AWS.stub('S3', 'getObject', function(params, callback) {
	callback(null, data);
	});
	app.useCallback(function(err, data) {
	assert.ifError(err, 'success');
	assert.equal(data, 'hello world');
	assert.equal(AWS.S3.callCount, 1, 'one s3 client created');
	assert.ok(AWS.S3.calledWithExactly({ region }), 's3 client created for the correct region');
	assert.equal(getObject.callCount, 1, 'called s3.getObject once');
	assert.ok(getObject.calledWith(expected), 'called s3.getObject with expected params');
	AWS.S3.restore();
	assert.end();
	});
	});