swap ape::mst for igraph::mst

[Jason Vander Heiden]

I don't think we need to add an ape dependency just for the mst function. There is an mst function in igraph, which we need anyway.

[Namita Gupta]

The reason is for convenience, as ape takes and returns a distance matrix. igraph takes and returns a graph object, which would need to be both created and then parsed in order to use that function.

[Jason Vander Heiden]

Yeah, I saw that. If it's something we can do only once with a couple extra lines, then maybe we should do it. But if it hasn't to be done repeatedly then we should keep the ape dependency.

[Jason Vander Heiden]

Don't think anyone cares about fixing this.