The release 1.1.0 introduced a BC change in the configuration semantics.
Before 1.1.0, if not explicitly provided, the value of authSource was set to the database name specified in the
connection section, or to admin if even the database name was empty.
With 1.1.0, if the authSource key is not set in the configuration, it won't be set in connection options either.
Take a look to CHANGELOG.md for further details.