Bump typed-ast requirement to 1.3.1, as 1.3.0 has a rare crash bug (p…

…ython#6344)

setup.py

@@ -169,7 +169,7 @@ def run(self):
                                         ]},
       classifiers=classifiers,
       cmdclass=cmdclass,
-      install_requires = ['typed-ast >= 1.3.0, < 1.4.0',
+      install_requires = ['typed-ast >= 1.3.1, < 1.4.0',
                           'mypy_extensions >= 0.4.0, < 0.5.0',
                           ],
       extras_require = {