Add missing import comment

[akshayjshah]

We let one exposed package sneak through without an import comment.
There's no practical way for anyone to be using with the wrong import
path, but let's clean up anyways.

[codecov]

Codecov Report

Merging #574 into master will increase coverage by 0.39%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #574      +/-   ##
==========================================
+ Coverage   97.06%   97.45%   +0.39%     
==========================================
  Files          39       39              
  Lines        2279     2001     -278     
==========================================
- Hits         2212     1950     -262     
+ Misses         59       43      -16     
  Partials        8        8

Impacted Files	Coverage Δ
buffer/buffer.go	100% <ø> (ø)	⬆️
zapcore/console_encoder.go	96.49% <0%> (-1.07%)	⬇️
zapcore/error.go	93.75% <0%> (-0.7%)	⬇️
stacktrace.go	97.87% <0%> (-0.44%)	⬇️
logger.go	94.49% <0%> (-0.36%)	⬇️
zapcore/memory_encoder.go	98.66% <0%> (-0.02%)	⬇️
writer.go	100% <0%> (ø)	⬆️
level.go	100% <0%> (ø)	⬆️
zapcore/json_encoder.go	100% <0%> (ø)	⬆️
zapcore/tee.go	100% <0%> (ø)	⬆️
... and 20 more

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