Update CHANGELOG for v0.13.0

[chfast]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.19%. Comparing base (9a31345) to head (981c36e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1026   +/-   ##
=======================================
  Coverage   94.19%   94.19%           
=======================================
  Files         149      149           
  Lines       15887    15887           
=======================================
  Hits        14964    14964           
  Misses        923      923           

Flag	Coverage Δ
eof_execution_spec_tests	17.25% <ø> (ø)
ethereum_tests	27.32% <ø> (ø)
ethereum_tests_silkpre	19.12% <ø> (ø)
execution_spec_tests	20.42% <ø> (ø)
unittests	88.96% <ø> (ø)

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