Use 'check' for argument to eventsOnLoggedOut

To prevent server exception:

```
I20141008-11:21:18.950(2)? Exception while invoking method 'eventsOnLoggedOut' Error: Did not check() all arguments during call to 'eventsOnLoggedOut'
I20141008-11:21:19.045(2)?     at _.extend.throwUnlessAllArgumentsHaveBeenChecked (packages/check/match.js:303)
I20141008-11:21:19.046(2)?     at Object.Match._failIfArgumentsAreNotAllChecked (packages/check/match.js:80)
I20141008-11:21:19.046(2)?     at maybeAuditArgumentChecks (packages/livedata/livedata_server.js:1485)
I20141008-11:21:19.046(2)?     at packages/livedata/livedata_server.js:650
I20141008-11:21:19.046(2)?     at _.extend.withValue (packages/meteor/dynamics_nodejs.js:37)
I20141008-11:21:19.046(2)?     at packages/livedata/livedata_server.js:649
I20141008-11:21:19.046(2)?     at _.extend.withValue (packages/meteor/dynamics_nodejs.js:37)
I20141008-11:21:19.047(2)?     at _.extend.protocol_handlers.method (packages/livedata/livedata_server.js:648)
I20141008-11:21:19.047(2)?     at packages/livedata/livedata_server.js:548
```