add array input to meta_query key

[hossin277]

use :

'meta_query' => array(
 'relation' => 'OR',
 array(
	 'key' => ['meta_key_1' , 'meta_key_2', 'meta_key_3'],
	 'value' => 23,
 ),
);

Instead of this :

'meta_query' => array(
 'relation' => 'OR',

 array(
	 'key' => 'meta_key_1',
	 'value' => 23,

 ), 
 array(
	 'key' => 'meta_key_2',
	 'value' => 23,

 ), 
 array(
	 'key' => 'meta_key_3',
	 'value' => 23,
 ), 
);

Trac ticket: https://core.trac.wordpress.org/ticket/55630