Update changelog for pending release (#308)

Update changelog for pending release

CHANGELOG.md

@@ -1,3 +1,17 @@
+# Release v1.5.0 (2021-06-25)
+
+### Smithy Go module
+* `time`: Update time parsing to not be as strict for HTTPDate and DateTime ([#307](https://github.com/aws/smithy-go/pull/307)) 
+  * Fixes [#302](https://github.com/aws/smithy-go/issues/302) by changing time to UTC before formatting so no local offset time is lost.
+
+### Codegen
+* Adds support for integrating client members via plugins ([#301](https://github.com/aws/smithy-go/pull/301))
+* Fix serialization of enum types marked with payload trait ([#296](https://github.com/aws/smithy-go/pull/296))
+* Update generation of API client modules to include a manifest of files generated ([#283](https://github.com/aws/smithy-go/pull/283))
+* Update Group Java group ID for smithy-go generator ([#298](https://github.com/aws/smithy-go/pull/298))
+* Support the delegation of determining the errors that can occur for an operation ([#304](https://github.com/aws/smithy-go/pull/304))
+* Support for marking and documenting deprecated client config fields. ([#303](https://github.com/aws/smithy-go/pull/303))
+
 # Release v1.4.0 (2021-05-06)
 
 ### Smithy Go module