Update 543_diameter_of_binary_tree.md

Author: Joseph Luce

leetcode/easy/543_diameter_of_binary_tree.md

@@ -2,8 +2,9 @@
 
 ## Best Solution
 - Runtime: O(N)
-- Space: O(N)
+- Space: O(H)
 - N = Number of nodes in binary tree
+- H = Height of the tree
 
 Take this binary tree example:
 ```