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

Merging #1463 (866c8cd) into master (95c3b7c) will not change coverage.
The diff coverage is n/a.

@@           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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