remove rational computation

[jverzani]

• remove unnecessary rational power

[codecov]

Codecov Report

Merging #251 (33243f2) into master (ae1be29) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #251   +/-   ##
=======================================
  Coverage   83.48%   83.48%           
=======================================
  Files          12       12           
  Lines        1968     1968           
=======================================
  Hits         1643     1643           
  Misses        325      325           

Impacted Files	Coverage Δ
src/find_zeros.jl	95.90% <100.00%> (ø)

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