tol_induced_tree -> tol_induced_subtree

Finally getting caught to Teams Ruby and Python on the tests, and turned up a disagreement in our function names. The 'induced tree' method is called `tol_induced_tree` in the existing tests and `tol_induced_subtree`[in the API](https://github.com/OpenTreeOfLife/opentree/wiki/Open-Tree-of-Life-APIs#tree_of_life). 

I don't mind changing the R libraries name, but think we've stuck with the API names in most cases?