Update scala-compiler to 2.12.15

[scala-steward]

Updates org.scala-lang:scala-compiler from 2.12.8 to 2.12.15.

I'll automatically update this PR to resolve conflicts as long as you don't change it yourself.

If you'd like to skip this version, you can just close this PR. If you have any feedback, just mention me in the comments below.

Configure Scala Steward for your repository with a .scala-steward.conf file.

Have a fantastic day writing Scala!

Files still referring to the old version number

The following files still refer to the old version number (2.12.8).
You might want to review and update them manually.

README.md

Ignore future updates

Add this to your .scala-steward.conf file to ignore future updates of this dependency:

updates.ignore = [ { groupId = "org.scala-lang", artifactId = "scala-compiler" } ]

labels: library-update, semver-patch, old-version-remains

[codecov]

Codecov Report

Merging #211 (1f93409) into master (3e83aab) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #211   +/-   ##
=======================================
  Coverage   88.73%   88.73%           
=======================================
  Files          18       18           
  Lines        1660     1660           
  Branches       11       11           
=======================================
  Hits         1473     1473           
  Misses        187      187           

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[scala-steward]

Superseded by #239.

[scala-steward]

Superseded by #248.