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.DMatrix.R

@@ -17,7 +17,6 @@
 #' xgb.DMatrix.save(dtrain, 'xgb.DMatrix.data')
 #' dtrain <- xgb.DMatrix('xgb.DMatrix.data')
 #' @export
-#' 
 xgb.DMatrix <- function(data, info = list(), missing = NA, ...) {
   if (typeof(data) == "character") {
     handle <- .Call("XGDMatrixCreateFromFile_R", data, as.integer(FALSE),