Updated docstrings to match style

Co-authored-by: Elias Carvalho <[email protected]>

Author: souma4

src/binarytree.jl

@@ -170,11 +170,11 @@ minnode(node::Nothing) = nothing
 """
   BinaryTrees.maxnode(tree)
 
-Find the `node` with the maximum `key` in the `tree`.
+Find the node with the maximum key in the `tree`.
 
   BinaryTrees.maxnode(node)
 
-Find the `node` with the maximum `key` in the subtree rooted at `node`.
+Find the node with the maximum key in the subtree rooted at `node`.
 If `nothing` is provided, `nothing` is returned.
 """
 maxnode(tree::BinaryTree) = maxnode(root(tree))