docs: modify mutable.shuffle example code and Go Playground links

[ebina4yaka]

Replaced the lom.Shuffle usage example and GO Playground code that was incorrect.
(Shuffle Playground was a compile error, Reverse Playground was old code using lo package)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.27%. Comparing base (0fa0632) to head (10811c2).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #595   +/-   ##
=======================================
  Coverage   94.27%   94.27%           
=======================================
  Files          18       18           
  Lines        3179     3179           
=======================================
  Hits         2997     2997           
  Misses        170      170           
  Partials       12       12           

Flag	Coverage Δ
unittests	94.27% <ø> (ø)

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