Barmode 'relative' does not place leading bar in correct quadrant

[etpinard]

First reported by @programflex in #475 (comment)

Reproducible example: http://codepen.io/etpinard/pen/bepzRm

May be related to #627

cc @keeganmccallum

[keeganmccallum]

Looking into, issue seems to be that -0 === 0, will make a pull request shortly

[etpinard]

@keeganmccallum You're the man!

[keeganmccallum]

#687

[etpinard]

will be fixed in fix-bar-relative-first-bucket.