Update python-igraph dependency

[penguinpee]

The package has been renamed to igraph and so has the importable
module. Package python-igraph is now legacy.

[szhorvat]

and so has the importable module

For clarification, the name of the module did not change, only the name of the package on PyPI. Of course, this has no impact on the contents of this PR.

[penguinpee]

and so has the importable module

For clarification, the name of the module did not change, only the name of the package on PyPI. Of course, this has no impact on the contents of this PR.

My apologies. I just looked at the wheel and the sdist of the latest release available for python-igraph. They are useless / broken in that they only contain metadata. Anyway, renaming the dependency will fix that.

[eleftherioszisis]

Thanks for catching it and for opening a PR!