Make go vet happy

examples/keyboard/keyboard/keyrects.go

@@ -1,4 +1,4 @@
-// Copyright 2013 Hajime Hoshi
+// Copyright 2013 The Ebiten Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

genkeys.go

@@ -264,10 +264,10 @@ func main() {
 		buildTag := ""
 		switch path {
 		case "internal/ui/keys_glfw.go":
-			buildTag = `// +build darwin,!arm,!arm64 linux windows
-// +build !js
-// +build !android
-// +build !ios`
+			buildTag = "// +build darwin,!arm,!arm64 linux windows" +
+				"\n// +build !js" +
+				"\n// +build !android" +
+				"\n// +build !ios"
 		case "internal/ui/keys_js.go":
 			buildTag = "// +build js"
 		}