Fixup heroku incorrectly identify redis url during asset compilation

Apparently the redis gem will try to a parse a url, works around the following error

```
-----> Writing config/database.yml to read from DATABASE_URL
-----> Preparing app for Rails asset pipeline
       Running: rake assets:precompile
       rake aborted!
       invalid url
       /tmp/build_b75e5e32-8137-4801-b8b1-17d4939c71cf/vendor/bundle/ruby/2.0.0/gems/redis-3.0.5/lib/redis/client.rb:338:in `_parse_options'
       /tmp/build_b75e5e32-8137-4801-b8b1-17d4939c71cf/vendor/bundle/ruby/2.0.0/gems/redis-3.0.5/lib/redis/client.rb:59:in `initialize'
       /tmp/build_b75e5e32-8137-4801-b8b1-17d4939c71cf/vendor/bundle/ruby/2.0.0/gems/redis-3.0.5/lib/redis.rb:30:in `new'
       /tmp/build_b75e5e32-8137-4801-b8b1-17d4939c71cf/vendor/bundle/ruby/2.0.0/gems/redis-3.0.5/lib/redis.rb:30:in `initialize'
       /tmp/build_b75e5e32-8137-4801-b8b1-17d4939c71cf/config/initializers/resque.rb:7:in `new'
       /tmp/build_b75e5e32-8137-4801-b8b1-17d4939c71cf/config/initializers/resque.rb:7:in `redis'
```