Update links to Scalafix documentation

[fthomas]

The old URLs are 404s now.

[codecov]

Codecov Report

Base: 82.42% // Head: 82.51% // Increases project coverage by +0.08% 🎉

Coverage data is based on head (6c52e49) compared to base (58ae9c9).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2842      +/-   ##
==========================================
+ Coverage   82.42%   82.51%   +0.08%     
==========================================
  Files         152      152              
  Lines        2947     2962      +15     
  Branches      215      188      -27     
==========================================
+ Hits         2429     2444      +15     
  Misses        518      518              

Impacted Files	Coverage Δ
.../scala/org/scalasteward/core/application/Cli.scala	99.37% <0.00%> (+0.06%)	⬆️

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