Doc-comment: Improve array @param

This uses syntax from https://phpstan.org/writing-php-code/phpdoc-types#general-arrays.

int[] means an array of ints with arbitrary keys (usually strings)
list<string> means an array of strings with sequential integer keys starting at 0
list<string>[] means an arbitrary array of string lists
list<string[]> means list of arbitrary string arrays
string[][] means two dimensional array with arbitrary keys in both dimensions
array was left in the comments for https://phpstan.org/writing-php-code/phpdoc-types#array-shapes

plugins/master-slave.php

@@ -10,7 +10,7 @@ class AdminerMasterSlave {
 	private $masters = array();
 
 	/**
-	* @param array [$slave => $master]
+	* @param string[] [$slave => $master]
 	*/
 	function __construct($masters) {
 		$this->masters = $masters;