Update Protobuf, remove upper constraint

requirements.txt

@@ -7,7 +7,7 @@ msgpack>=0.5.6
 sortedcontainers
 uvloop>=0.14.0
 grpcio-tools>=1.33.2
-protobuf>=3.12.2,<4.0.0
+protobuf>=3.20.3
 configargparse>=1.2.3
 multiaddr>=0.0.9
 pymultihash>=0.8.2

setup.py

@@ -157,7 +157,7 @@ setup(
     package_data={"hivemind": ["proto/*", "hivemind_cli/*"]},
     include_package_data=True,
     license="MIT",
-    setup_requires=["grpcio-tools"],
+    setup_requires=["grpcio-tools>=1.33.2"],
     install_requires=install_requires,
     extras_require=extras,
     classifiers=[