Update setup.py

Author: graingert

setup.py

@@ -17,7 +17,7 @@
     py_modules=["pytest_timeout"],
     entry_points={"pytest11": ["timeout = pytest_timeout"]},
     install_requires=["pytest>=5.0.0"],
-    python_requires='>=3.6',
+    python_requires=">=3.6",
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Environment :: Console",