Remove SSL3 entirely as default TLS level

gevent/_ssl2.py

@@ -399,7 +399,7 @@ def wrap_socket(sock, keyfile=None, certfile=None,
                      ciphers=ciphers)
 
 
-def get_server_certificate(addr, ssl_version=PROTOCOL_SSLv3, ca_certs=None):
+def get_server_certificate(addr, ssl_version=PROTOCOL_SSLv23, ca_certs=None):
     """Retrieve the certificate from the server at the specified address,
     and return it as a PEM-encoded string.
     If 'ca_certs' is specified, validate the server cert against it.

gevent/_ssl3.py

@@ -442,7 +442,7 @@ def wrap_socket(sock, keyfile=None, certfile=None,
                      ciphers=ciphers)
 
 
-def get_server_certificate(addr, ssl_version=PROTOCOL_SSLv3, ca_certs=None):
+def get_server_certificate(addr, ssl_version=PROTOCOL_SSLv23, ca_certs=None):
     """Retrieve the certificate from the server at the specified address,
     and return it as a PEM-encoded string.
     If 'ca_certs' is specified, validate the server cert against it.