function getFlags(node) {
			if (node.arguments.length < 2) {
				return "";
			}

			if (isString(node.arguments[1])) {
				return node.arguments[1].value;
			}

			return null;
		}
Gets flags of a regular expression created by the given `RegExp()` or `new RegExp()` call
Examples:
    new RegExp(".")         // => ""
    new RegExp(".", "gu")   // => "gu"
    new RegExp(".", flags)  // => null
@param {ASTNode} node `CallExpression` or `NewExpression` node
@returns {string|null} flags if they can be determined, `null` otherwise
@private