CI: continuous-integration/travis-ci/pr build fails due to unavailable channel
#### Problem description

**continuous-integration/travis-ci/pr** build currently seems to fail for everyone, regardless of PR. Error output below:

```
conda env create -q --file=ci/deps/travis-37.yaml
Collecting package metadata (repodata.json): ...working... failed
UnavailableInvalidChannel: The channel is not accessible or is invalid.
  channel name: c3i_test
  channel url: https://conda.anaconda.org/c3i_test
  error code: 404
You will need to adjust your conda configuration to proceed.
Use `conda config --show channels` to view your configuration's current state,
and use `conda config --show-sources` to view config file locations.
The command "ci/setup_env.sh" failed and exited with 1 during .
Your build has been stopped.

```