googlesheets4 1.1.1

• gs4_auth(subject =) is a new argument that can be used with
  gs4_auth(path =), i.e. when using a service account. The path and
  subject arguments are ultimately processed by
  gargle::credentials_service_account() and support the use of a service
  account to impersonate a normal user.

• gs4_scopes() is a new function to access scopes relevant to the Sheets and
  Drive APIs. When called without arguments, gs4_scopes() returns a named
  vector of scopes, where the names are the associated short aliases.
  gs4_scopes() can also be called with a character vector; any element that's
  recognized as a short alias is replaced with the associated full scope (#291).

• Various internal changes to sync up with gargle v1.5.0.