fix CI tests

Author: eulerkochy

src/DataStructures.jl

@@ -52,6 +52,7 @@ module DataStructures
 
     export RBTree, search_node, minimum_node
     export AVLTree, sorted_rank
+    export SplayTree, maximum_node
 
     export findkey
 

src/splay_tree.jl

@@ -178,7 +178,7 @@ function Base.delete!(tree::SplayTree{K}, d::K) where K
     return tree
 end
 
-function insert!(tree::SplayTree{K}, d::K) where K
+function Base.insert!(tree::SplayTree{K}, d::K) where K
     is_present = search_node(tree, d)
     if (is_present !== nothing) && (is_present.data == d)
         return tree