message: Avoid slicing a string in DocParsingError.
  Fixes
diff: @@ -422,12 +422,8 @@ pub enum DocParsingError {
  impl DocParsingError {
  /// Builds a NotJson DocParsingError
  fn invalid_json(invalid_json: &str) -> Self {
  - let sample_json: String = if invalid_json.len() < 20 {
  - invalid_json.to_string()
  - } else {
  - format!("{:?}...", &invalid_json[0..20])
  - };
  - DocParsingError::InvalidJson(sample_json)
  + let sample = invalid_json.chars().take(20).collect();
  + DocParsingError::InvalidJson(sample)
  }
  }
  @@ -793,6 +789,11 @@ mod tests {
  ))
  );
  }
  + {
  + // Short JSON, under the 20 char take.
  + let json_err = schema.parse_document(r#"{"count": 50,}"#);
  + assert_matches!(json_err, Err(InvalidJson(_)));
  + }
  {
  let json_err = schema.parse_document(
  r#"{
  