Update CHANGELOG.md: "Swift Next" -> "Swift 5.5"

Author: benrimmington

CHANGELOG.md

@@ -6,6 +6,7 @@ CHANGELOG
 
 | Version                | Released   | Toolchain   |
 | :--------------------- | :--------- | :---------- |
+| [Swift 5.5](#swift-55) |            |             |
 | [Swift 5.4](#swift-54) |            |             |
 | [Swift 5.3](#swift-53) | 2020-09-16 | Xcode 12.0  |
 | [Swift 5.2](#swift-52) | 2020-03-24 | Xcode 11.4  |
@@ -25,8 +26,8 @@ CHANGELOG
 
 </details>
 
-Swift Next
-----------
+Swift 5.5
+---------
 
 * [SE-0299][]:
 
@@ -8383,6 +8384,7 @@ Swift 1.0
 [SE-0296]: <https://github.com/apple/swift-evolution/blob/main/proposals/0296-async-await.md>
 [SE-0297]: <https://github.com/apple/swift-evolution/blob/main/proposals/0297-concurrency-objc.md>
 [SE-0298]: <https://github.com/apple/swift-evolution/blob/main/proposals/0298-asyncsequence.md>
+[SE-0299]: <https://github.com/apple/swift-evolution/blob/main/proposals/0299-extend-generic-static-member-lookup.md>
 
 [SR-75]: <https://bugs.swift.org/browse/SR-75>
 [SR-106]: <https://bugs.swift.org/browse/SR-106>