Pin VW, Gensim, and Scikit-learn versions

[juhoinkinen]

Pin versions:

• sklearn to 0.21.x
• gensim to 3.8.x
• vowpalwabbit probably to 8.7.x

At the moment fasttext(mirror) is not pinned, maybe wait for resolving #290 by merging PR #292?

Closes #291.

[osma]

I think we should pin fastText too, to the current version (fasttextmirror version 0.8.22). This way we are at least safe against unintended upgrades if fasttextmirror happens to change.

Unfortunately #292 is stuck currently due to a bug in the new fastText Python bindings. When we get around to merging that we should then update the pin to the new version.

[osma]

Looks good in general.

The pinned versions should probably be specified in setup.py too. For example, pip install annif[vw] should install VW 8.7, not some other version.

[codecov]

Codecov Report

Merging #317 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #317   +/-   ##
=======================================
  Coverage   99.37%   99.37%           
=======================================
  Files          55       55           
  Lines        2867     2867           
=======================================
  Hits         2849     2849           
  Misses         18       18

---

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 d67c082...c6e89cd. Read the comment docs.

[juhoinkinen]

Also pinned versions in Wiki page for fasttext and VW installation with pip.