Update ensemble.jl

src/ensemble.jl

@@ -19,7 +19,7 @@ dataset on which the ensembler should be trained on.
 function ensemble_weights(sol::EnsembleSolution, data_ensem)
     obs = first.(data_ensem)
     predictions = reduce(
-        vcat, reduce(hcat, [sol[i][s] for i in 1:length(sol)]) for s in obs)
+        vcat, reduce(hcat, [sol.u[i][s] for i in 1:length(sol)]) for s in obs)
     data = reduce(vcat,
         [data_ensem[i][2] isa Tuple ? data_ensem[i][2][2] : data_ensem[i][2]
          for i in 1:length(data_ensem)])