adapt envfit.coca to changes in vegan-to-be-2.2-0

'strata = NULL' is needed for missing strata in getPermuteMatrix
or you get an error:

> sol <- envfit(bp.sym, verges, which = "response")
Error in getPermuteMatrix(permutations, nr, strata = strata) :
  argument "strata" is missing, with no default
Calls: envfit -> envfit.coca -> vectorfit -> getPermuteMatrix
need importFrom(vegan, factorfit, vectorfit)
Merge pull request #1 from jarioksa/reconcile-with-vegan

Reconcile with vegan