Update README.md

fix typo

Author: brean

README.md

@@ -9,7 +9,7 @@ Currently there are 7 path-finders bundled in this library, namely:
 - Best-First
 - Bi-directional A\*
 - Breadth First Search (BFS)
-- Di-directional Breadth First Search (BFS)
+- Bi-directional Breadth First Search (BFS)
 - Iterative Deeping A\* (IDA\*)
 - Minimum Spanning Tree (MSP)