chore: prepare 6.0.0 release (#216)

Author: kangasta

CHANGELOG.md

@@ -5,6 +5,8 @@ See updating [Changelog example here](https://keepachangelog.com/en/1.0.0/)
 
 ## [Unreleased]
 
+## [6.0.0]
+
 ### Added
 - labels support for storages
 - support for network gateways
@@ -262,7 +264,8 @@ See updating [Changelog example here](https://keepachangelog.com/en/1.0.0/)
 
 First stable release
 
-[Unreleased]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v5.4.0...HEAD
+[Unreleased]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v6.0.0...HEAD
+[6.0.0]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v5.4.0...v6.0.0
 [5.4.0]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v5.3.1...v5.4.0
 [5.3.1]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v5.3.0...v5.3.1
 [5.3.0]: https://github.com/UpCloudLtd/upcloud-go-api/compare/v5.2.1...v5.3.0

upcloud/client/client.go

@@ -16,7 +16,7 @@ import (
 )
 
 const (
-	Version    string = "5.4.0"
+	Version    string = "6.0.0"
 	APIVersion string = "1.3"
 	APIBaseURL string = "https://api.upcloud.com"