Attempt to "fix" cache "sticking"

Attempt to address the issue of sessions "sticking" when used with MojoX::Security::Session.

This issue manifests when some requests (not reliably replicable) "stick" - the ``get`` call to ``memcached`` doesn't return and the mojolicious request times out. Subsequent calls then mostly just timeout.

Creating a new instance of ``Memcached::Client`` each request doesn't suffer from the issue but feels wrong currently.