Fix PHPDoc comments for update functions

[takotakot]

The return type of acf_update_metadata is integer|boolean .
See:

acf/includes/acf-meta-functions.php

Lines 166 to 169 in 368a956

	*
	* @return integer|boolean Meta ID if the key didn't exist, true on successful update, false on failure.
	*/
	function acf_update_metadata( $post_id = 0, $name = '', $value = '', $hidden = false ) {

This is necessary for type consistency with other functions.