Revert "requirements: do not install typed-ast for Python 3.8"

This reverts commit 4154a32.

Gets used in tests via `# flags: --python-version 2.7` etc.

Author: blueyed

setup.py

@@ -178,7 +178,7 @@ def run(self):
       classifiers=classifiers,
       cmdclass=cmdclass,
       # When changing this, also update test-requirements.txt.
-      install_requires=['typed-ast >= 1.3.5, < 1.4.0; python_version < "3.8"',
+      install_requires=['typed-ast >= 1.3.5, < 1.4.0',
                         'mypy_extensions >= 0.4.0, < 0.5.0',
                         ],
       # Same here.

test-requirements.txt

@@ -9,7 +9,7 @@ psutil>=4.0
 pytest>=4.4
 pytest-xdist>=1.22
 pytest-cov>=2.4.0
-typed-ast>=1.3.5,<1.4.0; python_version < '3.8'
+typed-ast>=1.3.5,<1.4.0
 typing>=3.5.2; python_version < '3.5'
 py>=1.5.2
 virtualenv