Fix typo on cache backend module

The correct module is 'dogpile.cache.memcached' and not
'dogpile.cache.memcache'.

Change-Id: Ie452c95dab4fcd04f65f6378c735490ee8cf4c70
Merge "Fix typo on cache backend module"
Imported Translations from Transifex

Change-Id: I39e917b54f7bfc795e0e5785189bbc0f1db5eda4