BF: conda: Temporary pin version in miniconda URL

[kyleam]

Our test suite is failing with the latest miniconda version (gh-443). The initial issue looks to be a version conflict. A reasonable approach would be to just bump all versions in that test because understanding or resolving this specific set of incompatibilities between old software versions isn't worth the time or effort.

But that won't work because our distributions.conda isn't compatible with the latest conda in at least two ways. We use an environment file that doesn't have an extension that conda now expects. That's an easy fix, and there's a patch in gh-443. The bigger issue is that environments seem to no longer have their own bin/conda unless conda is explicitly installed in the environment. (This mirrors the then seemingly hard-to-trigger problem initially described in gh-173.) As a result, our method for identifying an environment's root prefix is broken. Based on a quick scan of envs/NAME/, there may no longer be an easy way to map from an environment to its root prefix.

Given that there doesn't seem to be a quick fix and an always failing test suite makes it hard to spot other, unknown failures, let's get back to a passing state by pinning the miniconda version that we download.

[codecov[bot]]

Codecov Report

Merging #445 into master will increase coverage by 10.22%. The diff coverage is 100%.

@@             Coverage Diff             @@
##           master     #445       +/-   ##
===========================================
+ Coverage   78.81%   89.04%   +10.22%     
===========================================
  Files         148      148               
  Lines       11871    11871               
===========================================
+ Hits         9356    10570     +1214     
+ Misses       2515     1301     -1214

Impacted Files	Coverage Δ
reproman/distributions/tests/test_conda.py	100% <ø> (+30.12%)	:arrow_up:
reproman/distributions/conda.py	94.16% <100%> (+43.74%)	:arrow_up:
reproman/utils.py	86.84% <0%> (+0.49%)	:arrow_up:
formatters.py	86.5% <0%> (+0.61%)	:arrow_up:
reproman/interface/retrace.py	95.28% <0%> (+0.94%)	:arrow_up:
reproman/config.py	89.61% <0%> (+1.29%)	:arrow_up:
reproman/tests/utils.py	80.73% <0%> (+2.04%)	:arrow_up:
...eproman/interface/tests/test_backend_parameters.py	100% <0%> (+4.34%)	:arrow_up:
reproman/resource/tests/test_docker_container.py	100% <0%> (+5.4%)	:arrow_up:
reproman/tests/skip.py	97.53% <0%> (+6.17%)	:arrow_up:
... and 21 more

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