Fix missing arguments on _check_positive() calls

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@4f21d83). Click here to learn what that means. The diff coverage is 0%.

@@            Coverage Diff            @@
##             master      #14   +/-   ##
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  Coverage          ?   66.29%           
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  Files             ?        5           
  Lines             ?      178           
  Branches          ?       28           
=========================================
  Hits              ?      118           
  Misses            ?       46           
  Partials          ?       14

Impacted Files	Coverage Δ
trimeter/_impl.py	60.68% <0%> (ø)

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[njsmith]

thanks!