message: Use display for error message printing
diff: @@ -19,7 +19,7 @@ impl FromStr for ReplCommand {
  type Err = ParseError;
  fn from_str(src: &str) -> Result<ReplCommand, ParseError> {
  - grammar::parse_ReplCommand(src).map_err(|e| ParseError(format!("{:?}", e)))
  + grammar::parse_ReplCommand(src).map_err(|e| ParseError(format!("{}", e)))
  }
  }
  @@ -39,7 +39,7 @@ impl FromStr for Term {
  type Err = ParseError;
  fn from_str(src: &str) -> Result<Term, ParseError> {
  - grammar::parse_Term(src).map_err(|e| ParseError(format!("{:?}", e)))
  + grammar::parse_Term(src).map_err(|e| ParseError(format!("{}", e)))
  }
  }
  