Update transitionName props in readme to reflect they can also be an Object

[ldabiralai]

As per

trigger/src/index.js

Lines 65 to 68 in 899e456

	popupTransitionName: PropTypes.oneOfType([
	PropTypes.string,
	PropTypes.object,
	]),

trigger/src/index.js

Lines 83 to 86 in 899e456

	maskTransitionName: PropTypes.oneOfType([
	PropTypes.string,
	PropTypes.object,
	]),

popupTransitionName and maskTransitionNamecan be object as well as a string