Added chris-lea/redis-server PPA to Travis build

This is part of solving the problem that Ubuntu 12.04 tries to install v.2.2.x when running apt-get redis-server. Adding the chris-lea/redis-server PPA aims to get the latest version of the redis-server so including redis-server in /requirements/apt-packages.txt can pass the travis tests.
Added upgrade-redis-server.sh to travis build file
Added redis-server to file

redis-server is a requirement that's not currently included in the install script. This adds redis-server which will be pulled from the chris-lea/redis-server PPA to get the latest version. This avoids versioning conflicts with travis which is currently at 2.8.x but the Ubuntu Precise (12.04) package is at 2.2.x.
Added chris-lea/redis-server to install script

redis-server isn't included in the apt-packages. Adding the chris-lea/redis-server PPA gets the environment closer to the travis build which currently has v.2.8.x installed as default. The precise package using apt-get install redis-server is v.2.2.x which causes an error in the travis build.
Merge pull request #2 from craigappl/Fix-Redis-Server

Merging to see if it passes the travis tests