Error log when skipping duplicate files

[nikayou]

Because of Issue #13, I have to specify the option to skip duplicate files:
cpdSkipDuplicateFiles := true

It seems to work, but my SBT console displays each time errors:
[error] Skipping /home/file.scala since it appears to be a duplicate file and --skip-duplicate-files is set.

This should not be an error: that's the expected behaviour, and not having a spam of red log messages.