Fix "overriden" typo (#806)

Author: TimothyGu

index.bs

@@ -11148,7 +11148,7 @@ default interfaces do not have such steps.
     with [=identifier=] |id| and in [=Realm=] |realm|
     is <dfn lt="create an interface object">created</dfn> as follows:
 
-    1.  Let |steps| be |I|'s [=overriden constructor steps=] if they exist, or
+    1.  Let |steps| be |I|'s [=overridden constructor steps=] if they exist, or
         the following steps otherwise:
         1.  If |I| was not declared with a [=constructor operation=],
             then [=ECMAScript/throw=] a {{ECMAScript/TypeError}}.