Fix compile error in test suite.

Thanks for the new version - unfortunately the test suite doesn't compile for me: 

tests/Control/Timeout/Tests.hs:23:76:
    No instance for (Num (Positive NominalDiffTime))
      arising from the literal ‘1000’
    In the second argument of ‘(<)’, namely ‘1000’
    In the second argument of ‘suchThat’, namely ‘(< 1000)’
    In the second argument of ‘($)’, namely
      ‘suchThat arbitrary (< 1000)’

This change fixes it.