In the effort to make the arkworks framework available for compilation
in wasm environment, we need to make ``getrandom`` indirect dependency an
opt-in feature.
``rand/std`` feature triggers the dependency over ``getrandom``, so it can't be
included in the ``std`` feature. It must be separated in an extra
feature that we named ``getrandom``

getrandom being a dev-dependency makes cargo trying to include it in the
build even when we are trying to build with no-std.
Setting the resolver = "2" fixes the issue as Cargo is forced to
recompute all the dependencies.