Remove bundle cache scripts

Previously, the Travis configuration was set up to cache the bundled
gems on each build, which was actually causing the build to run more
slowly. Removed the scripts from the repository.

https://trello.com/c/NzWNFLuz
Update sample environment variables

Previously, some sensitive data was being stored in the application's
sample environment variables, which was presenting a security issue. The
variables have been updated to use dummy values.

https://trello.com/c/ss5habYR