Bug 1571567 - Fix no-fallthrough errors in /docshell. r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D40873

--HG--
extra : moz-landing-system : lando

docshell/test/mochitest/file_bug668513.html

@@ -87,9 +87,8 @@
         }
         step++;
         finish();
-      }
-      default:
         break;
+      }
     }
   }
 </script>