Negative values are not handled correctly

[liezlsantos]

When you have negative values in the dataset, the percentage is computed without using the absolute value of the data:

IMO, this wrong and the values are not represented correctly:

After adjusting min and max of the x-axis to -100 and 200, respectively (so we can see all the bars):

Suggestion:
Compute the percentage using absolute value of the data (for reference this is also how it is done in MS Excel):

I submitted a pull request.

[y-takey]

Hi @liezlsantos , sorry for the delay.
Thanks for your issue and nice suggestion. :) I agree your idea completely. so, merged PR #30 and published a newer npm module(v0.7.1).

thank you very much!

[liezlsantos]

Awesome! Thanks, @y-takey.