Updated docstrings to match style

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

Author: souma4

src/binarytree.jl

@@ -151,11 +151,11 @@ end
 """
   BinaryTrees.minnode(tree)
 
-Find the `node` with the smallest `key` in the `tree`.
+Find the node with the smallest key in the `tree`.
 
   BinaryTrees.minnode(node)
 
-Find the `node` with the smallest `key` in the subtree rooted at `node`.
+Find the node with the smallest key in the subtree rooted at `node`.
 If `nothing` is provided, `nothing` is returned.
 """
 minnode(tree::BinaryTree) = minnode(root(tree))