Add blank line after build rules, for human readability.
diff --git a/ninja_defs.go b/ninja_defs.go
index a653796..b87a38a 100644
--- a/ninja_defs.go
+++ b/ninja_defs.go
@@ -349,7 +349,7 @@
 		nw.Default(outputs...)
 	}
 
-	return nil
+	return nw.BlankLine()
 }
 
 func valueList(list []*ninjaString, pkgNames map[*PackageContext]string,