Add missing connect abstractmethod

telethon/network/connection/common.py

@@ -22,6 +22,10 @@ class Connection(abc.ABC):
         self._proxy = proxy
         self._timeout = timeout
 
+    @abc.abstractmethod
+    def connect(self, ip, port):
+        raise NotImplementedError
+
     @abc.abstractmethod
     def get_timeout(self):
         """Returns the timeout used by the connection."""