dotenv should be treated as a peerDependency and not as a dependency

[mohit-solutelabs]

most of us are using dotenv and then only we would need a dependency like this to solve the problem that your awesome package is solving.
Assuming that, we must not be using 2 versions of dotenv, as your package is treating it as a dependency, but if we treat it as a peer dependency, the users would not have 2 copies of dotenv in their app.

I will submit the PR this weekend. Thanks for this awesome package.