mark slices as valid for json marshalling

[jdeflander]

closes #197

[codecov]

Codecov Report

Merging #198 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master    #198   +/-   ##
======================================
  Coverage    96.3%   96.3%           
======================================
  Files           9       9           
  Lines        1111    1111           
======================================
  Hits         1070    1070           
  Misses         22      22           
  Partials       19      19

Impacted Files	Coverage Δ
util.go	92.3% <100%> (ø)	⬆️

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[jeevatkm]

@jdeflander Thanks for the PR.