Update the typed-ast dependency to 1.2.0 (#6190)

This should be cherry picked into the release branch (#6130)

setup.py

@@ -168,7 +168,7 @@ def run(self):
                                         ]},
       classifiers=classifiers,
       cmdclass=cmdclass,
-      install_requires = ['typed-ast >= 1.1.1, < 1.2.0',
+      install_requires = ['typed-ast >= 1.2.0, < 1.3.0',
                           'mypy_extensions >= 0.4.0, < 0.5.0',
                           ],
       extras_require = {

test-requirements.txt

@@ -8,7 +8,7 @@ psutil==5.4.0
 pytest>=3.4
 pytest-xdist>=1.22
 pytest-cov>=2.4.0
-typed-ast>=1.1.1,<1.2.0
+typed-ast>=1.2.0,<1.3.0
 typing>=3.5.2; python_version < '3.5'
 py>=1.5.2
 virtualenv