Missing pre-sign if balance is negative

[xstable]

I've played a bit around with your nice app. Thanks for sharing it here.

I've found that in case of negative balance the - is missing in front of the value. I've fixed this with my PR #24

BTW: If you cherish this PR, please add a label to the aprove of the PR named : 'hacktoberfest-accepted' Thanx.