Fix early return in MatrixClient.setGuestAccess

(as well as a similar bug in the test suite)

Turns out that `q.all(a, b)` === `q.all([a])`, rather than `q.all([a,b])`: it
only waits for the *first* promise - which means that `client.setGuestAccess`
would swallow any errors returned from the API.

src/client.js

@@ -2153,7 +2153,7 @@ MatrixClient.prototype.setGuestAccess = function(roomId, opts) {
         });
     }
 
-    return q.all(readPromise, writePromise);
+    return q.all([readPromise, writePromise]);
 };
 
 // Registration/Login operations