Fixed the failing test where server crashes on disconnect involving connectBuffer

Source of bug: after connection to nsp '/', the socket's connectBuffer
was being deleted. On attempt to reconnect to a different namespace,
the connect buffer was deleted and we attempted to push to it. Instead
of the deleting the connect buffer, it is now emptied.
Merge pull request #1682 from kevin-roark/fix/disconnect-connectbuffer-crash

Fixed the failing test where server crashes on disconnect involving connectBuffer
package: bump `engine.io`
Merge branch 'master' of github.com:Automattic/socket.io