Fix typo in field extractor (splices -> slices)

[bvwells]

No description provided.

[codecov-io]

Codecov Report

Merging #287 into master will increase coverage by 0.49%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #287      +/-   ##
==========================================
+ Coverage   73.27%   73.77%   +0.49%     
==========================================
  Files          42       42              
  Lines        1564     1590      +26     
==========================================
+ Hits         1146     1173      +27     
  Misses        365      365              
+ Partials       53       52       -1     

Impacted Files	Coverage Δ
tags/fieldextractor.go	85.29% <ø> (ø)
tracing/opentracing/id_extract.go	85.18% <0.00%> (-5.73%)	⬇️
retry/retry.go	76.24% <0.00%> (-1.11%)	⬇️
auth/metadata.go	100.00% <0.00%> (ø)
retry/options.go	80.48% <0.00%> (ø)
recovery/interceptors.go	100.00% <0.00%> (ø)
logging/zap/ctxzap/context.go	0.00% <0.00%> (ø)
logging/zap/client_interceptors.go	100.00% <0.00%> (ø)
logging/zap/server_interceptors.go	100.00% <0.00%> (ø)
logging/logrus/client_interceptors.go	100.00% <0.00%> (ø)
... and 7 more

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[johanbrandhorst]

Thanks for your contribution! Could you cherry pick this against v2 as well?

[bvwells]

@johanbrandhorst thanks for the review and merge. I've opened up a PR on the V2 branch with the cherry picked commit.