Outdated CONDA_VERSION causes PRs to fail

[osteele]

PR #67 fails in a way that's unrelated to the content of the change.

I would expect based on the Travis log that any other PR will also fail, and that re-building the master branch will also fail.

The cause is that the Dockerfile specifies ENV CONDA_VERSION 4.4.10, but the latest Miniconda version as shown on https://repo.continuum.io/miniconda/ is 4.5.4. This causes assert current.headers['etag'] == latest.headers['etag'] in test_dependencies.py to fail.