hubot/Dockerfile.template: Change 'REDISCLOUD_URL' -> 'REDIS_URL'
hubot/Dockerfile.template: Change 'REDISCLOUD_URL' -> 'REDIS_URL'

hubot-scripts has supported this since 48a3b142 (Added REDIS_URL to
support dokku, 2014-03-01).  It still doesn't match Docker's
REDIS_PORT, but it's more generic than the provider-specific
REDISCLOUD_URL.

ostree/dockerfile,wking/dockerfile,fr34k8/dockerfile