Re-enable parallelism for Python 3.5
Re-enable parallelism for Python 3.5

mhils/hyper-h2,vladmunteanu/hyper-h2,bhavishyagopesh/hyper-h2,python-hyper/hyper-h2,python-hyper/hyper-h2,vladmunteanu/hyper-h2,Kriechi/hyper-h2,Kriechi/hyper-h2