install dep if missing during buffalo setup for dep app

[markbates]

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (development@097f506). Click here to learn what that means.
The diff coverage is 0%.

@@              Coverage Diff               @@
##             development    #1371   +/-   ##
==============================================
  Coverage               ?   48.64%           
==============================================
  Files                  ?       92           
  Lines                  ?     4070           
  Branches               ?        0           
==============================================
  Hits                   ?     1980           
  Misses                 ?     1985           
  Partials               ?      105

Impacted Files	Coverage Δ
buffalo/cmd/setup.go	4.48% <0%> (ø)

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