fix one more ref to semiannual

[wleescor]

was going to submit similar to pull request #403 but got beaten to it. seemed to be missing one more file still

[codecov-commenter]

Codecov Report

Base: 83.92% // Head: 83.92% // No change to project coverage 👍

Coverage data is based on head (48fdd79) compared to base (f100640).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #410   +/-   ##
=======================================
  Coverage   83.92%   83.92%           
=======================================
  Files          50       50           
  Lines        4448     4448           
  Branches      729      729           
=======================================
  Hits         3733     3733           
  Misses        513      513           
  Partials      202      202           

Flag	Coverage Δ
unittests	83.92% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
chainladder/development/learning.py	73.87% <100.00%> (ø)

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[jbogaardt]

Thank you again @wleescor!