The graphviz library is supposed to be installed according to issue #66.
However, it cannot be used:
Maybe the -dev/-devel version is missing or pkg-config?
I disabled this for my docs for now but would be nice to have it on. Happy to test again.
I went ahead and installed graphviz-dev, if you can test again.
Sorry it took so long to get back to you :(
Install graphviz-dev, refs #449.
Closing this for now, please reopen if it doesn't fix it.