Small doc grammar fix

[thomcc]

Accidentally missed there was a nit in #1155 before landing. This addresses it.

[codecov]

Codecov Report

Merging #1156 (a4a6bde) into master (46def6d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1156   +/-   ##
=======================================
  Coverage   78.18%   78.18%           
=======================================
  Files          47       47           
  Lines        5932     5932           
=======================================
  Hits         4638     4638           
  Misses       1294     1294           

Impacted Files	Coverage Δ
src/lib.rs	89.64% <ø> (ø)

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