So, I heard you need Drupal and memcached running in Travis, right? But you have this "little" issue that Travis/Drupal cannot connect to memcached, something like:

Before you jump into docs and tutorials on how to install memcached in Travis, probably it's already there, you just have to enable.

Simply add a new php.ini file somewhere in your source, for example in travis_scripts/php.ini:

 extension = "memcached.so"

and point that from your Travis, for example from your before_install section:

phpenv config-add travis_scripts/php.ini

Or even better, from your setup_environment.sh or equivalent

Your error should have gone now.