fix W1Test.hs to work with QuickCheck-2.7.6
fix W2Test.hs to work withQuickCheck-2.7.6
fix W3Test.hs to work with QuickCheck-2.7.6
fix W4Test.hs to work with QuickCheck-2.7.6
fix W5Test.hs to work with QuickCheck-2.7.6
W5 Ex 1: fix test, add solution