TST: test_read_clipboard_infer_excel warning
```
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_read_clipboard_infer_excel
  /home/travis/build/jreback/pandas/pandas/io/clipboards.py:63: ParserWarning: Falling back to the 'python' engine because the 'c' engine does not support regex separators (separators > 1 char and different from '\s+' are interpreted as regex); you can avoid this warning by specifying engine='python'.
    return read_table(StringIO(text), sep=sep, **kwargs)
```