tests: remove duplicate lines from docker_env_vars.sh
collector: add better logging on bad response from collector
express: handle case where transaction may not exist
collector: Add a test of parsing a non-JSON server response
http: Only clone http options/headers when the 'Expect' header is present.

Hits the aggressive 'middle' branch of this logic less often, and no
longer interferes with defineProperty-happy libraries like `riak.js`
docs: updated for new version
release: published 1.14.3