Use $REDIS_URL environment variable if set

[sumanthratna]

1. update CHANNEL_LAYERS
   

   live/hacktj_live/settings.py

   Lines 95 to 116 in cb65a3a

   	CHANNEL_LAYERS = {
   	"default": {"BACKEND": "channels.layers.InMemoryChannelLayer"},
   	}
   	if in_docker:
   	CHANNEL_LAYERS = {
   	"default": {
   	"BACKEND": "channels_redis.core.RedisChannelLayer",
   	"CONFIG": {
   	"hosts": [("redis", 6379)],
   	"symmetric_encryption_keys": [SECRET_KEY],
   	},
   	},
   	}
   	elif is_nc_available and run_cmd(["nc", "-z", "127.0.0.1", "6379"]).returncode == 0:
   	CHANNEL_LAYERS = {
   	"default": {
   	"BACKEND": "channels_redis.core.RedisChannelLayer",
   	"CONFIG": {
   	"hosts": [("127.0.0.1", 6379)],
   	},
   	},
   	}

2. add heroku-redis buildpack (and update app.json)