set seed to get reproducible results when creating the README.md

Author: bblodfon

README.Rmd

@@ -102,7 +102,8 @@ Please open an issue so we can add your package.
 Some learners need to have their variable importance measure "activated" during learner creation.
 For example, to use the "impurity" measure of Random Forest via the {ranger} package:
 
-```{r }
+```{r}
+set.seed(0)
 task = tsk("iris")
 lrn = lrn("classif.ranger")
 lrn$param_set$values = list(importance = "impurity")