use security/py-cryptodome
don't limit protobuf version to 3

Index: steam.egg-info/requires.txt
--- steam.egg-info/requires.txt.orig
+++ steam.egg-info/requires.txt
@@ -1,5 +1,5 @@
 six>=1.10
-pycryptodomex>=3.7.0
+pycryptodome>=3.7.0
 requests>=2.9.1
 vdf>=3.3
 cachetools>=3.0.0
@@ -18,4 +18,4 @@ gevent-eventemitter~=2.1
 protobuf<3.18.0
 
 [client:python_version >= "3"]
-protobuf~=3.0
+protobuf
