Fix environment key error

[TheRusskiy]

Is there an error in the docs? They say to use the env key, while in the code it's environment

The code:
https://github.com/skylightio/skylight-ruby/blob/9072ec33878ac6d6b9987c5a5a527e8460e35c2c/lib/skylight/config.rb#L280

https://www.skylight.io/support/environments#2-require-and-start-the-skylight-agent-in-each-of-your-desired-environments

[zvkemp]

Thanks for the PR @TheRusskiy! It looks like you are correct, at least in one sense. Part of the confusion comes from a general overloading of the environment term; in Skylight.start! it is used to select the environment-specific values from your yaml config, but does not specify the environment on Skylight.io into which data is reported. We are going to re-consider how these terms are used and hopefully will come up with a clearer way to differentiate these concepts. I'm going to leave this PR open in the meantime, we will re-address it when we've made some decisions.