Update SRF 'format=graph' to use GraphViz extension version 1.1+.

Also update SRF composer.json to suggest mediawiki/graphviz.
During testing, I observed $text to be a page name, from which the old code made a URL.  The new version of GraphViz handles a page name directly without need for conversion to a URL.  For reference: https://www.mediawiki.org/wiki/Extension:GraphViz#Links