message: Include `+` for crates.io feature requirements
  This change was introduced in commit of rust-lang/crates.io.
diff: @@ -87,7 +87,7 @@ optional dependencies. This allows packages to internally enable/disable
  features without requiring a new dependency.
  > **Note**: [crates.io] requires feature names to only contain ASCII letters,
  -> digits, `_`, or `-`.
  +> digits, `_`, `-`, or `+`.
  ### Usage in end products
  