Update setup.py to include python 3.7 instead of 3.5

Author: marcharper

setup.py

@@ -29,8 +29,8 @@
     include_package_data=True,
     package_data={"": ["axelrod/data/*.csv"]},
     classifiers=[
-        "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3 :: Only",
     ],
     python_requires=">=3.5",