[R] replace uses of T and F with TRUE and FALSE (#5778)

* [R-package] replace uses of T and F with TRUE and FALSE

* enable linting

* Remove skip

Co-authored-by: Philip Hyunsu Cho <chohyu01@cs.washington.edu>

R-package/vignettes/xgboostPresentation.Rmd

@@ -363,7 +363,7 @@ xgb.plot.importance(importance_matrix = importance_matrix)
 You can dump the tree you learned using `xgb.dump` into a text file.
 
 ```{r dump, message=T, warning=F}
-xgb.dump(bst, with_stats = T)
+xgb.dump(bst, with_stats = TRUE)
 ```
 
 You can plot the trees from your model using ```xgb.plot.tree``