Not returning explicitly anything on Prim's algo

[jordanmontt]

Currently, our Prim's algo implementation explicitly returns in the method run. See AIPrim>>#run. The last line it returns the edges. This breaks the API convention for all the other algos. If one checks, all of the other algos they do not explicitly return anything. We need to update the Prim's algo to not explicitly return in the run method but rather having a method called reconstructPath like in AIBFS for example.

[jordanmontt]

@dkgoutham