readEnv updates system env

[JohnJ255]

I spent a lot of time to understand why docker run --rm --env-file test.env myimage go test ./... use variables from .env, but docker run --rm --env-file test.env myimage env shows variables from test.env
Therefore my algorithm to load config based on loading config.yml, then rewrite by variables from the .env and then rewrite by variables from a system... But the cleanenv library rewrites system environments on reading config from .env file!!!
Be careful...