update x-cloak CSS to allow conditional disabling

[browner12]

change the suggested x-cloak CSS to specifically only target the boolean x-cloak attribute or the attribute with an empty string value (x-cloak="").

this means we will no longer target the attribute when it has a non-empty string value (x-cloak="off").

the benefit this gives is we can conditionally disable the cloaking for elements we know will be visible immediately. this prevents a "blip in" from the hidden to visible state.

Here is a Blade example to show how it would work:

<div
    x-show="jsCondition"
    x-cloak="{{ $condition ? 'off' : '' }}"
>Alpine Rocks</div>

this works because, given these elements:

<div x-cloak></div>
<div x-cloak=""></div>
<div x-cloak="off"></div>

we get this behavior:

CSS Selector	Matches
[x-cloak]	all three
[x-cloak=""]	first two only
[x-cloak="off"]	third only

---

This is already possible by conditionally showing the x-cloak, but I think this solution provides a better looking code.

<div
    x-show="jsCondition"
    @if($condition)
        x-cloak
    @endif
>Alpine Rocks</div>