change label in directory

Author: triuyen

DIRECTORY.md

@@ -105,7 +105,7 @@
     * [Word Break](https://github.com/TheAlgorithms/Rust/blob/master/src/dynamic_programming/word_break.rs)
   * Financial
     * [Present Value](https://github.com/TheAlgorithms/Rust/blob/master/src/financial/present_value.rs)
-    * [Present Value](https://github.com/TheAlgorithms/Rust/blob/master/src/financial/black_scholes.rs)
+    * [Black Scholes](https://github.com/TheAlgorithms/Rust/blob/master/src/financial/black_scholes.rs)
   * General
     * [Convex Hull](https://github.com/TheAlgorithms/Rust/blob/master/src/general/convex_hull.rs)
     * [Fisher Yates Shuffle](https://github.com/TheAlgorithms/Rust/blob/master/src/general/fisher_yates_shuffle.rs)