Updated to latest version (2.0.0) of memcached module

Memory leak had been identified in 0.2.8 per [this issue](https://github.com/3rd-Eden/node-memcached/issues/186).

```
catbox-memcached [master>] $ npm test

> catbox-memcached@1.0.3 test /Users/julian/dev/catbox-memcached
> make test-cov


  ..................................................

50 tests complete
Test duration: 85 ms
No global variable leaks detected
Coverage: 100.00%
```