Instructions for setting up environment variables are wrong

[campbellbartlett]

In the set-up instructions for the speedy docker image (/speedy/docker/speedy/readme.md) it states that the environment variable to set the influxDB name should be:
SPEEDY_DB_NAME

However in index.js, it is reading the environment variable from:
process.env.INFLUXDB_DB

This should be updated to match, either in the readme or in the index.js file. I am happy to open a PR with the change, but not sure which you would prefer changed (considering any backwards compatibility you might want for anyone currently using the image).