[3.x] Fetch reset token explicitly.

[syntheticminds]

With a route like the following, $token in showResetForm(Request $request, $token = null) will give the value of {subdomain} and not {token} because route parameters are injected based on their order.

Route::group(['domain' => '{subdomain}.example.com'], function () {
    $this->get('password/reset/{token}', 'Auth\ResetPasswordController@showResetForm')->name('password.reset');
});

This pull request proposes that the token is explicitly fetched by name to avoid this.

I have submitted this to the master branch because it could break sites that do not use Auth::routes() where {token} is the standard parameter name.