dynamic sbt-scalafix version

[mzuehlke]

Retrieve the latest sbt-scalafix plugin version from coursier (versionCache) instead of relying on a hardcoded version.

Fixes #2357

[fthomas]

This is great!

[mzuehlke]

Thanks for the comments @fthomas
I'm not sure how to get the test reliable. Depending on wether the data is in the cache or not the executed command are different. One idea wold be to run the cmd sbtAlg.runMigration... twice.
The 1st to make sure the cache is properly filled but don't look at the state afterwards and the 2nd to assert the expect change. Doesn't look that nice. Or reduce the TTL to 0 then we in tests always expect value to be written to the cache. But this would make the test slower....

[fthomas]

Another option could be to add a
/tmp/scala-steward/workspace/store/versions/v2/https/repo1.maven.org/maven2/ch/epfl/scala/sbt-scalafix_2.12_1.0/versions.json to the initial MockState so that VersionsCache always reads the versions from that file.

[codecov]

Codecov Report

Merging #2475 (bd096e8) into master (b0699bf) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2475      +/-   ##
==========================================
+ Coverage   81.11%   81.20%   +0.08%     
==========================================
  Files         142      142              
  Lines        2468     2479      +11     
  Branches       41       59      +18     
==========================================
+ Hits         2002     2013      +11     
  Misses        466      466              

Impacted Files	Coverage Δ
...a/org/scalasteward/core/buildtool/sbt/SbtAlg.scala	98.11% <100.00%> (+0.15%)	⬆️
.../org/scalasteward/core/buildtool/sbt/package.scala	100.00% <100.00%> (ø)

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[bjaglin]

Cool feature! Does this pick up RC releases as well? I am curious to know if/how I could test the impact of https://github.com/scalacenter/sbt-scalafix/releases/tag/v0.10.0-RC1 (particularly for scalacenter/sbt-scalafix#292).