Update Binary_Tree_Inorder_Traversal.java

/*
 * Given a binary tree, return the inorder traversal of its nodes' values.

 For example:
 Given binary tree {1,#,2,3},

 1
 \
 2
 /
 3
 return [1,3,2].

 Note: Recursive solution is trivial, could you do it iteratively?

 confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.
 */