findFormButton() is case sensitive when search for attributes

[beckenkamp]

When getFormField() tries to find form button with findFormButton() it throws ElementNotFoundException. This happens when the button have type attribute setted as "Submit" instead of "submit".

I understand that it is a stupid thing set element attributes like that example, but I gues I should report this anyway...

foreach ($xpath->query('descendant::input | descendant::button', $root) as $node) {
    if ('button' == $node->nodeName || in_array($node->getAttribute('type'), array('submit', 'button', 'image'))) {
        return $node;
    }
}

When I added "Submit" at the in_array() function, showed above, to test, it worked. Maybe we can add a strtolower() in $node->getAttribute('type') to solve this.

[aik099]

I can confirm that at least canSubmitForm method of the driver doesn't do case-insensitive type attribute check.

[aik099]

Can you please send a PR, where all usages of type attribute in the driver would be lowercased before doing any comparisons?

And another PR should go to Mink repository to update test fixtures to have type attributes with different case to catch that problem in all drivers at once.