Please depend on `igraph` instead of `python-igraph`

Hello,

For a while now igraph has been using name `igraph` instead of `python-igraph` on PyPI. Could you please update the name you use when specifying dependencies? I believe the change needs to be made in two places here:

https://github.com/search?q=repo%3AKrishnaswamyLab%2Fgraphtools+python-igraph&type=code

Please see https://github.com/igraph/python-igraph/issues/699 for more details.