[R] maintenance Nov 2017; SHAP plots (#2888)

* [R] fix predict contributions for data with no colnames

* [R] add a render parameter for xgb.plot.multi.trees; fixes #2628

* [R] update Rd's

* [R] remove unnecessary dep-package from R cmake install

* silence type warnings; readability

* [R] silence complaint about incomplete line at the end

* [R] initial version of xgb.plot.shap()

* [R] more work on xgb.plot.shap

* [R] enforce black font in xgb.plot.tree; fixes #2640

* [R] if feature names are available, check in predict that they are the same; fixes #2857

* [R] cran check and lint fixes

* remove tabs

* [R] add references; a test for plot.shap

R-package/R/xgb.plot.tree.R

@@ -95,7 +95,8 @@ xgb.plot.tree <- function(feature_names = NULL, model = NULL, trees = NULL, plot
     label     = dt$label,
     fillcolor = dt$filledcolor,
     shape     = dt$shape,
-    data      = dt$Feature)
+    data      = dt$Feature,
+    fontcolor = "black")
   
   edges <- DiagrammeR::create_edge_df(
     from  = match(dt[Feature != "Leaf", c(ID)] %>% rep(2), dt$ID),