old_contents: telegram_callback = {
      "type": "object",
      "properties": {
          "message": {
              "type": "object",
              "properties": {
                  "chat": {
                      "type": "object",
                      "properties": {
                          "id": {"type": "number"},
                          "type": {"enum": ["group", "private"]},
                          "title": {"type": "string"},
                          "username": {"type": "string"}
                      },
                      "required": ["id", "type"]
                  },
                  "text": {"type": "string"}
              },
              "required": ["chat", "text"]
          }
      },
      "required": ["message"]
  }
  
new_contents: telegram_callback = {
      "type": "object",
      "properties": {
          "message": {
              "type": "object",
              "properties": {
                  "chat": {
                      "type": "object",
                      "properties": {
                          "id": {"type": "number"},
                          "type": {"enum": ["group", "private", "supergroup"]},
                          "title": {"type": "string"},
                          "username": {"type": "string"}
                      },
                      "required": ["id", "type"]
                  },
                  "text": {"type": "string"}
              },
              "required": ["chat", "text"]
          }
      },
      "required": ["message"]
  }
  
subject: Handle supergroups. Fixes #123