Simplified the Travis build matrix
Simplified the Travis build matrix

Testing on different versions of CssSelector is not really worth it given
the test being performed, so let's reduce the Travis load a bit.
Refs #444

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