CORE-69: scala, sbt, plugins updates

[davidangb]

Jira: https://broadworkbench.atlassian.net/browse/CORE-69

Updates Scala, sbt, sbt plugins, and the scala-sbt docker image. Makes some very minor syntax tweaks to address syntax that was previously allowed but in the new version of Scala is now illegal. Updates scalatest and mockito-scala-scalatest.

This consolidates Scala Steward PRs #343, #281, #322, #323, #327, #288, #289.

---

• Submitter: Make sure Swagger is updated if API changes
• Submitter: If updating admin endpoints, also update firecloud-admin-cli
• Submitter: Update FISMA documentation if changes to:
  • Authentication
  • Authorization
  • Encryption
  • Audit trails
• Submitter: If you're adding new libraries, sign us up to security updates for them

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.65%. Comparing base (b9f7620) to head (ffbb8fa).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #350      +/-   ##
===========================================
- Coverage    59.87%   59.65%   -0.22%     
===========================================
  Files           18       18              
  Lines          638      637       -1     
  Branches        65       72       +7     
===========================================
- Hits           382      380       -2     
- Misses         256      257       +1     

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