Update to Maven 3.8.6 and sync used JDK version in DroneCI and SDKMan

[bmarwell]

• Supersedes: Update to Maven 3.8.6 #53 and [BUILD][#24] update drone build #55
• Fixes: Update Drone Image so that git is also inside container #24

[codecov-commenter]

Codecov Report

Base: 68.27% // Head: 68.27% // No change to project coverage 👍

Coverage data is based on head (4533dd8) compared to base (78c5e72).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #58   +/-   ##
=========================================
  Coverage     68.27%   68.27%           
  Complexity       40       40           
=========================================
  Files            10       10           
  Lines           186      186           
  Branches         10       10           
=========================================
  Hits            127      127           
  Misses           51       51           
  Partials          8        8           

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[sparsick]

Thank you @bmarwell