Unitalicize "log" in big O notation (apple#17)

Author: AustinConlon

Guides/Partition.md

@@ -74,13 +74,13 @@ extension Collection {
 ### Complexity
 
 The existing partition is an O(_n_) operations, where _n_ is the length of the
-range to be partitioned, while the stable partition is O(_n log n_). Both
+range to be partitioned, while the stable partition is O(_n_ log _n_). Both
 partitions have algorithms with improved performance for bidirectional
 collections, so it would be ideal for those to be customization points were they
 to eventually land in the standard library.
 
 `partitioningIndex(where:)` is a slight generalization of a binary search, and
-is an O(_log n_) operation for random-access collections; O(_n_) otherwise.
+is an O(log _n_) operation for random-access collections; O(_n_) otherwise.
 
 ### Comparison with other languages