Update HTTP/2 support in extras_require (#1799)

* Update extras_require

* Update setup.py

Author: tomchristie

setup.py

@@ -63,7 +63,7 @@ def get_packages(package):
         "async_generator; python_version < '3.7'"
     ],
     extras_require={
-        "http2": "h2==3.*",
+        "http2": "h2>=3,<5",
         "brotli": "brotlicffi==1.*",
     },
     classifiers=[