[8.x] Align Collection::pluck()/Arr:pluck() DocBlock with data_get()

[AegirLeet]

Arr::pluck() supports int and null for its $value param in addition the the already documented string|array, because it calls data_get() under the hood, which supports those types. Collection::pluck() just forwards the call to Arr:pluck(), so it supports the same types.

This PR aligns the DocBlocks to reflect this.

For reference, data_get() DocBlock:

framework/src/Illuminate/Collections/helpers.php

Lines 35 to 43 in 8a6bf87

	/**
	* Get an item from an array or object using "dot" notation.
	*
	* @param mixed $target
	* @param string|array|int|null $key
	* @param mixed $default
	* @return mixed
	*/
	function data_get($target, $key, $default = null)