Fix rubocop "where range"

[Splines]

I ran

bundle exec rubocop --autocorrect --disable-uncorrectable

which did not correct anything. After that, I ran

bundle exec rubocop -A

which corrected the three occurrences you see in this PR. Note that those corrections are unsafe due to this. Also see the Rails style guide here.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (dev@948e7ca). Learn more about missing BASE report.

Files	Patch %	Lines
app/models/medium.rb	0.00%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             dev     #675   +/-   ##
======================================
  Coverage       ?   53.09%           
======================================
  Files          ?      153           
  Lines          ?     6614           
  Branches       ?        0           
======================================
  Hits           ?     3512           
  Misses         ?     3102           
  Partials       ?        0           

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