Fixed the file upload tests on windows
Fixed the file upload tests on windows

Some drivers are expecting the path to the file to use the right directory
separator, unlike PHP which accepts / on all platforms.
Applying realpath on the path will normalize this on Windows.

Chekote/Mink,minkphp/Mink,talib570/Mink,jhedstrom/Mink,stof/Mink,jordi12100/Mink,jordi12100/Mink,Behat/Mink,talib570/Mink,jhedstrom/Mink,minkphp/Mink,Chekote/Mink,aik099/Mink