Correct accidental use of Array.prototype.every on an Object.

Fixes the error reported in the 1.6.1 pull request. (Thanks, @yorrd!)

It's worth nothing that the `DDP._allSubscriptionsReady` function which
was broken is used by the deprecated `spiderable` package.  Since
`spiderable` is deprecated, it's advisable to look into ways to stop
depending on it.

Refs: https://github.com/meteor/meteor/pull/9274#issuecomment-345358178.

packages/ddp-client/common/namespace.js

@@ -1,8 +1,14 @@
 import { DDPCommon } from 'meteor/ddp-common';
 import { Meteor } from 'meteor/meteor';
+import { keys } from "meteor/ddp-common/utils.js";
 
 import { Connection } from './livedata_connection.js';
 
+// This array allows the `_allSubscriptionsReady` method below, which
+// is used by the `spiderable` package, to keep track of whether all
+// data is ready.
+const allConnections = [];
+
 /**
  * @namespace DDP
  * @summary Namespace for DDP-related methods/classes.
@@ -78,11 +84,10 @@ DDP.onReconnect = callback => {
 // Hack for `spiderable` package: a way to see if the page is done
 // loading all the data it needs.
 //
-allConnections = [];
 DDP._allSubscriptionsReady = () => {
   return allConnections.every(conn => {
-    return conn._subscriptions.every(sub => {
-      return sub.ready;
+    return keys(conn._subscriptions).every(id => {
+      return conn._subscriptions[id].ready;
     });
   });
 };