Do not depend on chat package from en_us.go

Language generator should either compare PkgName with "en-us" or Name
with "en_us". I chose "Name" here.

data/lang/downloader.go

@@ -124,7 +124,7 @@ func readLang(name string, r io.Reader) {
 	tmpl := template.Must(template.New("code_template").Parse(
 		`// Code generated by downloader.go; DO NOT EDIT. 
 package {{.Name}}
-{{if ne .PkgName "en_us"}}
+{{if ne .Name "en_us"}}
 import "github.com/Tnze/go-mc/chat"
 
 func init() { chat.SetLanguage(Map) }