Update dotenv semver range

[cemremengu]

Closes #46

[cemremengu]

@mcollina I don't have permission for this one

[mcollina]

I don't have publish rights either.

@allevo can you add me to https://www.npmjs.com/package/fastify-env owners? So I'll put this in the npm org.

Also, who are daaaaa and jgiola on npm? They can publish releases to npm but they don't have write access to this repo. I'm fine in them being maintainer, as long as they have write access here as well.

[allevo]

They are my colleagues.

I've add you to the fastify-env project

[mcollina]

Add them to this repo as well ;).