MNT add python 3.8 as supported version

Author: glemaitre

setup.py

@@ -33,7 +33,8 @@
                'Operating System :: Unix',
                'Operating System :: MacOS',
                'Programming Language :: Python :: 3.6',
-               'Programming Language :: Python :: 3.7']
+               'Programming Language :: Python :: 3.7',
+               'Programming Language :: Python :: 3.8']
 INSTALL_REQUIRES = [
     'numpy>=1.11',
     'scipy>=0.17',