Apply updates from cookiecutter

This automated commit applies the latest updates from our cookiecutters [1] to
this repo.

[1]: https://github.com/hypothesis/cookiecutters

tox.ini

@@ -18,7 +18,6 @@ setenv =
     dev: SENTRY_ENVIRONMENT = {env:SENTRY_ENVIRONMENT:dev}
     dev: NEW_RELIC_APP_NAME = {env:NEW_RELIC_APP_NAME:gh-pr-upsert}
     dev: NEW_RELIC_ENVIRONMENT = {env:NEW_RELIC_ENVIRONMENT:dev}
-    dev,tests,functests: PYTHONDEVMODE = {env:PYTHONDEVMODE:1}
     tests: COVERAGE_FILE = {env:COVERAGE_FILE:.coverage.{envname}}
 passenv =
     HOME