Fix declared dependencies from merge issue

[chingor13]

This direct dependency was added in #288, but the presubmit check was not yet set up. It was already being transitively pulled in via google-auth-library-oauth2-http

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@9b14268). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #291   +/-   ##
=========================================
  Coverage          ?   78.79%           
  Complexity        ?      340           
=========================================
  Files             ?       21           
  Lines             ?     1495           
  Branches          ?      162           
=========================================
  Hits              ?     1178           
  Misses            ?      238           
  Partials          ?       79

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