Appeasing Rubocop violation
Appeasing Rubocop violation

```console
lib/browse_everything/driver/dropbox.rb:19:11: C: \
  Layout/IndentationWidth: Use 2 (not 0) spaces for rails indentation.
          def klass_for(metadata)
```

Per Rails conventions, the `private` method call requires methods
defined within the private scope to be indented 2 spaces.

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