Two group unpaired mean difference - negative values

[sunghunbae]

In the dabestr pacakge 0.3.0 version,
When both groups have negative values, the unpaired_mean_diff plot on the right side shows a wrong mean difference value.
For example, if one group values are around -330 and the other group values are around -300, then the unpaired mean diff plot shows -630 as a mean difference.

[josesho]

Hi, this has been noted in #30 and is being looked at. Thanks!