Redis overcommit_memory

[hfagerlund]

From terminal output of `$ ./vendor/bin/sail up ':

quiz_app-redis-1 
# WARNING Memory overcommit must be enabled! Without it, a background save or replication may fail under 
low memory condition. Being disabled, it can can also cause failures without low memory condition, see 
https://github.com/jemalloc/jemalloc/issues/1328. To fix this issue add 'vm.overcommit_memory = 1'
to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.

[hfagerlund]

Solved directly on the host system (ie. no PR required) by doing the following:

$ cd /etc/
$ sudo gedit sysctl.conf
## added the line below:
## vm.overcommit_memory = 1

## instead of restart, ran the following in a new (terminal) tab:
$ sudo sysctl vm.overcommit_memory=1

Verified that the warning no longer appeared in next run of ./vendor/bin/sail up.