Log Message:
(www/R-gargle) Updated 1.5.0 to 1.5.2

# gargle 1.5.2

* Fixed a bug in an internal helper that validates input specifying a service
  account. The helper targets a common mistake where the JSON for an OAuth
  client is provided to an argument that is meant for a service account (#270).

# gargle 1.5.1

* Completed some overlooked, unfinished work around the OAuth "app" to \ 
"client"
  transition that affected out-of-bound auth (#263, #264).

* The `secret_*()` functions are more discoverable via documentation.