Updated docstrings to match style

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

Author: souma4

src/binarytree.jl

@@ -189,10 +189,10 @@ maxnode(node::Nothing) = nothing
 """
   BinaryTrees.prevnext(tree, k)
 
-Returns a `tuple` of each `node` immediately before
-and after the `node` with `key`, `k` within `tree`.
+Returns a tuple of each node immediately before
+and after the `tree` node with key `k`.
 
-If an adjacent `node` does not exist, `nothing` is returned in its place.
+If an adjacent node does not exist, `nothing` is returned in its place.
 If `k` is `nothing`, returns `(nothing, nothing)`.
 """
 function prevnext(tree::BinaryTree, k)