Add update command

[dvdmuckle]

Fixes #116.

[codecov-io]

Codecov Report

Merging #117 into master will decrease coverage by 0.32%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #117      +/-   ##
==========================================
- Coverage   52.06%   51.73%   -0.33%     
==========================================
  Files          52       53       +1     
  Lines        1888     1900      +12     
==========================================
  Hits          983      983              
- Misses        879      891      +12     
  Partials       26       26

Impacted Files	Coverage Δ
commands/command.go	65.45% <ø> (ø)	:arrow_up:
commands/update.go	0% <0%> (ø)

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[kimtore]

Thanks, appreciated :)