press an element in one call to avoid timeouts

each browser.find* suffers from the standard splinter timeout of 2 seconds
this introduces unnecessary delay if you don't match the first condition
e.g. if you change default timeout to 10s and element is not found
you will have to wait 1 minute for this step to execute

this change should do exactly the same while not incurring any additional timeouts
Merge pull request #8 from antych/press-xpath

press an element in one call to avoid timeouts