message: added {} to the definition of SystemError::Unknown
diff: @@ -19,7 +19,7 @@ pub enum SystemError {
  InvalidRequest { error: String, request: Binary },
  InvalidResponse { error: String, response: Binary },
  NoSuchContract { addr: HumanAddr },
  - Unknown,
  + Unknown {},
  UnsupportedRequest { kind: String },
  }
  @@ -41,7 +41,7 @@ impl std::fmt::Display for SystemError {
  String::from_utf8_lossy(response.as_slice())
  ),
  SystemError::NoSuchContract { addr } => write!(f, "No such contract: {}", addr),
  - SystemError::Unknown => write!(f, "Unknown system error"),
  + SystemError::Unknown {} => write!(f, "Unknown system error"),
  SystemError::UnsupportedRequest { kind } => {
  write!(f, "Unsupported query type: {}", kind)
  }
  