update changelog and bump version

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Change log
 
+## v0.28.0
+- **BREAKING**: Changed a few things in the `ApolloCodegen` library to use `object.apollo.extensionMethod` syntax rather than `object.apollo_extensionMethod`. There's a few things that are still using `apollo_` notation due to constraints around conditional conformance, but you should particularly check your swift scripts for changes around `FileManager` APIs. ([#1183](https://github.com/apollographql/apollo-ios/pull/1183))
+- **BREAKING**: `NormalizedCache` now has a method for explicitly clearing the cache synchronously, in addition to the existing method to clear it asynchronously. If you've got a custom `NormalizedCache` implementation, you'll need to add an implementation for this method. ([#1186](https://github.com/apollographql/apollo-ios/pull/1186))
+- Fixed race conditions in `URLSessionClient` that were causing unexpected behavior. Turns out concurrency is hard! ([#1227](https://github.com/apollographql/apollo-ios/pull/1227))
+- Improved handling of a dependent key update cancelling an in-flight server fetch on a watcher. ([#1156](https://github.com/apollographql/apollo-ios/pull/1156))
+- Added option to Swift Codegen to pass in a prefix for custom scalars. ([#1216](https://github.com/apollographql/apollo-ios/pull/1216))
+
 ## v0.27.1
 - Better defense against multithreading crashes in `URLSessionClient`. ([#1184](https://github.com/apollographql/apollo-ios/pull/1184))
 - Fix for watchOS availability for `URLSessionClient`. ([#1175](https://github.com/apollographql/apollo-ios/pull/1175))

Configuration/Shared/Project-Version.xcconfig

@@ -1 +1 @@
-CURRENT_PROJECT_VERSION = 0.27.1
+CURRENT_PROJECT_VERSION = 0.28.0