relax another tolerance in test

Author: ablaom

test/regression/digits.jl

@@ -90,6 +90,6 @@ n_trees = 10
 n_folds = 5
 partial_sampling = 0.5
 r2 = nfoldCV_forest(Y, X, n_folds, n_subfeatures, n_trees, partial_sampling; verbose=false)
-@test mean(r2) > 0.6
+@test mean(r2) > 0.55
 
 end # @testset