update java version in maven-compiler-plugin

[advasileva]

Update Java version from 8 to 11. Closes #71

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PR-Codex overview

This PR updates the project's compiler version from Java 8 to Java 11.

Detailed summary

• Updated the source and target versions for the maven-compiler-plugin in pom.xml from 8 to 11.

[codecov-commenter]

Codecov Report

Merging #73 (1dbfac1) into master (f3eab25) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #73   +/-   ##
=========================================
  Coverage     73.52%   73.52%           
  Complexity       11       11           
=========================================
  Files             6        6           
  Lines            68       68           
  Branches          5        5           
=========================================
  Hits             50       50           
  Misses           18       18           

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[advasileva]

@volodya-lombrozo I updated the java version to 11, but the project stopped being assembled due to the IllegalArgumentException of qulice -- https://github.com/objectionary/speco/actions/runs/4271509780/jobs/7436026079#step:11:4252. I don't really understand what the problem is, maybe you have encountered this error?

[volodya-lombrozo]

@advasileva Looks like it's a quite old problem.

[advasileva]

@volodya-lombrozo This advice from Mikhail helped hide errors in the ide. Of course, it's better to fix the original problem with qulice