Do not append to cached bar files

[heyrict]

This will make headers recognized as data by pandoc in the next read.

Closes #23.

[RahulVadisetty91]

There are two calls to to_csv() for full_bars with the same parameters. You likely want only one call. Remove the redundant line.

keep the following line
full_bars.to_csv(self.output_path, header=header, index=False)