chore: prepare 6.4.0 release (#250)

Author: kangasta

CHANGELOG.md

@@ -5,6 +5,8 @@ See updating [Changelog example here](https://keepachangelog.com/en/1.0.0/)
 
 ## [Unreleased]
 
+## [6.4.0]
+
 ### Added
 - client functions `NewDefaultHTTPClient` and `NewDefaultHTTPTransport` to provide HTTP client default properties
 - kubernetes: experimental support for deleting nodes from node groups
@@ -317,7 +319,8 @@ See updating [Changelog example here](https://keepachangelog.com/en/1.0.0/)
 
 First stable release
 
-[Unreleased]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.3.2...HEAD
+[Unreleased]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.4.0...HEAD
+[6.4.0]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.3.2...v6.4.0
 [6.3.2]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.3.1...v6.3.2
 [6.3.1]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.3.0...v6.3.1
 [6.3.0]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.2.0...v6.3.0

upcloud/client/client.go

@@ -15,7 +15,7 @@ import (
 )
 
 const (
-	Version    string = "6.3.2"
+	Version    string = "6.4.0"
 	APIVersion string = "1.3"
 	APIBaseURL string = "https://api.upcloud.com"