Fix broken image in permutations README (Fixes trekhleb#2049)

Author: sowmya-rebbavarapu

src/algorithms/sets/permutations/README.md

@@ -29,7 +29,7 @@ n * (n-1) * (n -2) * ... * 1 = n!
 When repetition is allowed we have permutations with repetitions.
 For example the the lock below: it could be `333`.
 
-![Permutation Lock](https://www.mathsisfun.com/combinatorics/images/combination-lock.jpg)
+![Permutation Lock](./images/permutations-lock.png)
 
 **Number of combinations**