Update travis ruby version.
Provide default values if API keys missing.

This prevents carrierwave from blowing up when the environment
variables aren't set. If we precompile assets the rails app is
initialized even though we won't be uploading files with carrierwave
so there is no need to set the environment variables.
Vendor gems as part of build process.

Installing the package should not need to re-bundle all of the gems.

Since some of the gems have to be compiled the architecture can't be
"all" anymore.
Include bundler gem with package.

When installing the .deb package it no longer needs to install
anything from rubygems (everything is included).
Ignore any .env files.
Specify the database credentials in env variables.
Start unicorn web server.