Improve Lipogram

[sozelfist]

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Checklist:

• [x] I ran bellow commands using the latest version of rust nightly.
• [x] I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• [x] I ran cargo fmt just before my last commit.
• [x] I ran cargo test just before my last commit and all tests passed.
• [x] I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• [x] I added my algorithm to DIRECTORY.md with the correct link.
• [x] I checked COUNTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.38%. Comparing base (d0f258a) to head (4fa11e8).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #821   +/-   ##
=======================================
  Coverage   95.38%   95.38%           
=======================================
  Files         311      311           
  Lines       22626    22628    +2     
=======================================
+ Hits        21581    21583    +2     
  Misses       1045     1045           

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