Used enum instead of string for the signature scheme type

Author: JohanMabille

connectionfile-spec/connectionfile.schema.json

@@ -11,7 +11,7 @@
             "required": ["signature_scheme", "key"],
             "properties": {
                 "signature_scheme": {
-                    "type": "string",
+                    "enum": ["hmac-md5","hmac-sha256","hmac-sha512"],
                     "description": "scheme used to sign the messages"
                 },
                 "key": {
@@ -34,23 +34,23 @@
                     "description": "ip of the machine where the kernel runs"
                 },
                 "shell_port": {
-                    "type": "string",
+                    "type": ["integer","string"],
                     "description": "port used by the shell channel"
                 },
                 "control_port": {
-                    "type": "string",
+                    "type": ["integer","string"],
                     "description": "port used by the control channel"
                 },
                 "stdin_port": {
-                    "type": "string",
+                    "type": ["integer","string"],
                     "description": "port used by the stdin channel"
                 },
                 "hb_port": {
-                    "type": "string",
+                    "type": ["integer","string"],
                     "description": "port used by the heartbeat channel"
                 },
                 "iopub_port": {
-                    "type": "string",
+                    "type": ["ingerer","string"],
                     "description": "port used by the iopub channel"
                 }
             }