Check implementation on how to address self-to-self edges

[vc1492a]

https://github.com/adidier17/AuthorRank/blob/5a5912ea7ad3d3c2bf93d69c8b7dc7f881fee78d/author_rank/graph.py#L68

The current implementation does not allow for self-to-self edges in the graph since a co-authorship network is being created. We ought to re-read the original manuscript and verify whether this approach is in line with the original work.

[vc1492a]

Upon re-examining the original manuscript, this implementation seems correct and can be utilized in the code-base. More specifically, the authors note that a directed-graph is created in which each edge connects a pair of authors, A and B, and never an author to ones-self (e.g. A to A).