Upgrades Scala/Sbt/sbt-microsites

[juanpedromoreno]

This PR brings some minor upgrades such as scala, sbt or sbt-microsites. Also:

• Switches oraclejdk8 by openjdk8.
• Fixes the documentation link URL in the microsite.

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (prototyping@807d17a). Click here to learn what that means. The diff coverage is n/a.

@@              Coverage Diff               @@
##             prototyping      #64   +/-   ##
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  Hits                   ?      364           
  Misses                 ?      152           
  Partials               ?        0

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[vil1]

That's neat, thanks!