Specs: forgot return type for registerElement()

sky/specs/modules.md

Index: sky/specs/modules.md
diff --git a/sky/specs/modules.md b/sky/specs/modules.md
index a3d75f2afedc8926b0d041da3e501063e5b56902..3a8d3fe6b262367bb6c21796886c2b9b5766161b 100644
--- a/sky/specs/modules.md
+++ b/sky/specs/modules.md
@@ -103,7 +103,7 @@ abstract class AbstractModule extends EventTarget {
   List<Module> getImports(); // O(N)
   // returns the Module objects of all the imported modules
 
-  external registerElement(String tagname, Type elementClass); // O(1)
+  external void registerElement(String tagname, Type elementClass); // O(1)
   // registers a tag name with the parser
   // only useful during parse time
   // verify that tagname isn't null or empty