Empty env_vars removes all existing env_vars

[Doggie52]

TL;DR

Passing an empty env_vars removes all existing environment variables and leaves you with a GCF with no environment variables. Is this intentional? If it is, I think that should be made more clear in the readme.

Expected behavior
Leaving existing variables in place.

Observed behavior
Environment variables removed.

[bharathkkb]

Thanks for the report @Doggie52
This is intended behavior as we expect users to maintain the function config in git. We should definitely update the docs to call this out. Happy to review a PR too.

[Doggie52]

Sure, have raised #40.