Update index.md

[LY025714]

The name of class LengthTool is 'Length', but LengthTool.name is 'LengthTool' in Version 3.x

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 20.16%. Comparing base (95c3b7c) to head (866c8cd).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1463   +/-   ##
=======================================
  Coverage   20.16%   20.16%           
=======================================
  Files         287      287           
  Lines       10102    10102           
  Branches     2060     2060           
=======================================
  Hits         2037     2037           
  Misses       6852     6852           
  Partials     1213     1213           

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