Run "dot -c" on Heroku-16
Run "dot -c" on Heroku-16

To create config6 file (in $install_dir/usr/lib/graphviz). This file
lists the enabled plugins, and without this file, Graphviz cannot be
used, because there are no enabled plugins.

On Cedar-14, the file config6 exists already in /usr/lib/graphviz.

weibeld/heroku-buildpack-graphviz