Fix typo in Heap Sort README lg -> log

Heap Sort/README.markdown

@@ -42,7 +42,7 @@ As you can see, the largest items are making their way to the back. We repeat th
 
 > **Note:** This process is very similar to [selection sort](../Selection%20Sort/), which repeatedly looks for the minimum item in the remainder of the array. Extracting the minimum or maximum value is what heaps are good at.
 
-Performance of heap sort is **O(n lg n)** in best, worst, and average case. Because we modify the array directly, heap sort can be performed in-place. But it is not a stable sort: the relative order of identical elements is not preserved.
+Performance of heap sort is **O(n log n)** in best, worst, and average case. Because we modify the array directly, heap sort can be performed in-place. But it is not a stable sort: the relative order of identical elements is not preserved.
 
 Here's how you can implement heap sort in Swift: