Update lib version dependencies (for DiagrammeR mainly)

Fix @export tag in each R file (for Roxygen 5, otherwise it doesn't work anymore)
Regerate Roxygen doc

R-package/R/xgb.save.raw.R

@@ -16,7 +16,6 @@
 #' bst <- xgb.load(raw)
 #' pred <- predict(bst, test$data)
 #' @export
-#' 
 xgb.save.raw <- function(model) {
   if (class(model) == "xgb.Booster"){
     model <- model$handle