remove double 'or' string in runtime error

[alibaltschun]

Reference Issue

What does this implement/fix? Explain your changes.

removing double string 'of' in runtime error

Any other comments?

[codecov]

Codecov Report

Merging #600 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #600   +/-   ##
=======================================
  Coverage   98.92%   98.92%           
=======================================
  Files          85       85           
  Lines        5310     5310           
=======================================
  Hits         5253     5253           
  Misses         57       57

Impacted Files	Coverage Δ
imblearn/over_sampling/_smote.py	97.81% <ø> (ø)	⬆️

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[glemaitre]

Thanks