Update CHANGELOG.md for SE-0045 (Swift 3.1)

Author: benrimmington

CHANGELOG.md

@@ -1,6 +1,6 @@
 Note: This is in reverse chronological order, so newer entries are added to the top.
 
-Swift 3.0
+Swift 3.1
 ---------
 
 * [SE-0045](https://github.com/apple/swift-evolution/blob/master/proposals/0045-scan-takewhile-dropwhile.md)
@@ -10,6 +10,9 @@ Swift 3.0
   satisfying a predicate.  `drop(while:)` is used to request the subsequence
   remaining after dropping the longest subsequence satisfying a predicate.
 
+Swift 3.0
+---------
+
 * [SE-0136](https://github.com/apple/swift-evolution/blob/master/proposals/0136-memory-layout-of-values.md) and [SE-0101](https://github.com/apple/swift-evolution/blob/master/proposals/0101-standardizing-sizeof-naming.md)
 
   The functions `sizeof()`, `strideof()`, and `alignof()` have been removed.