Temporarily peg miniconda3 to version 4.6.14

[Balandat]

There seems to be an issue with the most recent miniconda 3 docker container, see discussion here: https://discuss.circleci.com/t/conda-not-found-in-miniconda-docker-image/32075

This temporarily pegs the miniconda container to the old version until this gets resolved upstream.

[facebook-github-bot]

@Balandat has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[codecov-io]

Codecov Report

Merging #246 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #246   +/-   ##
=======================================
  Coverage   99.95%   99.95%           
=======================================
  Files          63       63           
  Lines        2338     2338           
=======================================
  Hits         2337     2337           
  Misses          1        1

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3d75d97...690d5dd. Read the comment docs.

[facebook-github-bot]

@Balandat has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@Balandat has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[Balandat]

A new miniconda image has been released that reverts this change: https://discuss.circleci.com/t/conda-not-found-in-miniconda-docker-image/32075

Currently it appears unclear what anaconda's plan is for this, so we should keep an eye open.