Memcached instead of Memcache in the doc

[jrouillard]

Typo in cache config examples where "Memcached" is written instead of "Memcache" on the website and here. "Memcached" does not seem to work.

For instance:

https://github.com/UnionOfRAD/manual/blob/062a85b2823fd06c1e28bb13381742c59b2e6574/09_common_tasks/05_caching.md#configuration