39: Improve solution for Rust track exercise "Reverse String".

Dependencies

• [2] FOFFISFH 38: Add solution for Rust track exercise "Reverse String".
• [3] QK6XE5XF 13: Add Rust track exercises "Beer Song", "Proverb", "Difference Of Squares", "Sum Of Multiples", "Grains", "Prime Factors", "Armstrong Numbers" and "Reverse String".

Change contents

• edit in rust/reverse-string/src/lib.rs at line 1
  [3.7642]

  [3.7643]
  + use unicode_segmentation::UnicodeSegmentation;

  +
• replacement in rust/reverse-string/src/lib.rs at line 4
  [3.7683]→[2.386:417](∅→∅)
  − input.chars().rev().collect()
  [3.7683]

  [3.7744]
  + input.graphemes(true).rev().collect()
• edit in rust/reverse-string/Cargo.toml at line 2
  [3.11541]

  [3.11541]
  + unicode-segmentation = "1.8"