message: Fix gramm are
diff: @@ -373,13 +373,20 @@ fn check_for_duplicate_names(manifest: &Manifest) -> Result<(), failure::Error>
  }
  }
  }
  - let duplicate_names = duplicate_names
  + let duplicate_name_string = duplicate_names
  + .clone()
  .into_iter()
  .collect::<Vec<String>>()
  .join(", ");
  let duplicate_message = match duplicate_names.len() {
  - 1 => Some(format!("this name is duplicated: {}", duplicate_names)),
  - n if n >= 2 => Some(format!("these names are duplicated: {}", duplicate_names)),
  + 1 => Some(format!(
  + "this name is duplicated: {}",
  + duplicate_name_string
  + )),
  + n if n >= 2 => Some(format!(
  + "these names are duplicated: {}",
  + duplicate_name_string
  + )),
  _ => None,
  };
  match duplicate_message {
  