Update url for Cadence 1.0 migration guide

[chasefleming]

Closes #1400

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ac54f1c) 40.51% compared to head (b5ec241) 40.51%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1401   +/-   ##
=======================================
  Coverage   40.51%   40.51%           
=======================================
  Files          47       47           
  Lines        2589     2589           
=======================================
  Hits         1049     1049           
  Misses       1416     1416           
  Partials      124      124           

Flag	Coverage Δ
unittests	40.51% <ø> (ø)

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