Tests: restrict the version of numpy for py2

NumPy versions after 0.16 are not usable with python 2.

Author: Linkid

setup.py

@@ -63,5 +63,5 @@
         'Cython >= 0.27',
     ],
     test_suite="tests",
-    tests_require=['pytest', 'numpy'],
+    tests_require=['pytest', 'numpy<1.17'],
 )