Golint (#548)

* linter fixes

* Golint and format code

* fmt

directives_generate.go

@@ -59,6 +59,7 @@ func genImports(file, pack string, mi map[string]string) {
 		outs += "\n"
 	}
 
+	outs += "// Include all middleware.\n"
 	for _, v := range mi {
 		outs += `_ "` + v + `"` + "\n"
 	}
@@ -114,5 +115,5 @@ func fatalIfErr(err error) {
 const (
 	middlewarePath = "github.com/coredns/coredns/middleware/"
 	middlewareFile = "middleware.cfg"
-	header         = "// generated by directives_generate.go; DO NOT EDIT\n"
+	header         = "// generated by directives_generate.go; DO NOT EDIT\n\n"
 )