Update socket exceptions (#3127)

* error is an alias for OSError in Python 3
* herror and gaierror can be constructed without arguments (tested
  in Python 2.7 and 3.7)
* timeout uses the same arguments as herror and gaierror

Author: srittau

stdlib/2and3/socket.pyi

@@ -481,17 +481,19 @@ else:
 
 
 # ----- exceptions -----
-class error(IOError):
-    ...
+if sys.version_info < (3,):
+    class error(IOError): ...
+else:
+    error = OSError
 
 class herror(error):
-    def __init__(self, herror: int, string: str) -> None: ...
+    def __init__(self, herror: int = ..., string: str = ...) -> None: ...
 
 class gaierror(error):
-    def __init__(self, error: int, string: str) -> None: ...
+    def __init__(self, error: int = ..., string: str = ...) -> None: ...
 
 class timeout(error):
-    ...
+    def __init__(self, error: int = ..., string: str = ...) -> None: ...
 
 
 # Addresses can be either tuples of varying lengths (AF_INET, AF_INET6,