Arrows pointing in wrong direction for path to root visualizations

[jvendetti]

Originally reported by @cmungall as part of ncbo/bioportal_web_ui#62. Relocating to this repository, which houses the code responsible for BioPortal's visualizations.

To reproduce, go to the Classes page for any ontology and select any class in the tree with subclasses. Click the Visualization tab and note that the visualization type initially show is "Path to Root" (as indicated in the drop down box in the top-left corner of the visualization pane). The arrows point downward from the root to the leaf node, instead of pointing upward from the leaf to the root.