Fix typo in `digraph_disconnect`
Fix typo in `digraph_disconnect`

This commit fixes a typo in `digraph_disconnect` (in `src/digraph.c`),
whereby the edge table was being accessed when the adjacency matrix
should have been.

jmcph4/jcrl,jmcph4/jcrl,jmcph4/jcrl,jmcph4/jcrl