Enable an existing API Key.

def enable_key(self):
        """Enable an existing API Key."""
        print("This command will enable a disabled key.")
        apiKeyID = input("API Key ID: ")
        try:
            key = self._curl_bitmex("/apiKey/enable",
                                    postdict={"apiKeyID": apiKeyID})
            print("Key with ID %s enabled." % key["id"])
        except:
            print("Unable to enable key, please try again.")
            self.enable_key()