Update Selenium driver for Mink from 1.3.1 to 1.4.0 in acceptance tests

Since version 1.4.0 the Selenium driver for Mink uses again the element
on which the value was set (see
https://github.com/minkphp/MinkSelenium2Driver/pull/286

). When creating
a new folder or renaming one sending a new line ("\r") caused the
element on which the value was set to be removed, so the element was no
longer attached to the DOM when the driver tried to use it again, and
thus a "StaleElementReference" exception was thrown.

Due to this now it is needed to explicitly click the confirm button when
creating a new folder. In the case of the renaming, on the other hand,
nothing else besides not sending the new line is needed, as the Selenium
driver now unfocuses the element (that is why it uses again the element
after setting the value) which triggers the renaming.

Besides that, the Selenium driver for Mink uses a library to simulate
certain events, bitovi/syn. In version 1.4.0 that library was updated to
version 0.0.3, which seems to somehow break pressing the "escape" key.
Due to this now the sharing menu has to be closed by pressing "enter" on
the share menu button instead.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>