fix(Server): Do not warn if `STENCILA_SERVER_KEY` env var is set
fix(Server): Do not warn if `STENCILA_SERVER_KEY` env var is set

Closes #1439.

stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila