Update external dependencies to dose 3.2-rc1 and ocamlgraph 1.8.5

*** DO NOT MERGE THIS PR YET *** *** DO NOT MERGE THIS PR YET ***

Update external dependencies, moving to recent version of Dose+Cudf+Ocamlgraph, in preparation for the new release of Dose 3.2 and Cudf 0.7 that are impending.

Before merging, changes will need to be made to the Travis test environment, once the new version of the dose and cudf package will be on opam-repository.

To ensure a smooth transition, I want to collect feedback from the Travis output here, even if surely polluted by errors coming from unaligned versions of dose+cudf+ocamlgraph in the test environment.