Upgrade to Scala 2.12

[manuzhang]

Be sure to do all of the following to help us incorporate your contribution
quickly and easily:

• Make sure the commit message is formatted like:
  [GEARPUMP-<Jira issue #>] Meaningful description of pull request
• Make sure tests pass via sbt clean test.
• Make sure old documentation affected by the pull request has been updated and new documentation added for new functionality.

[codecov]

Codecov Report

Merging #2106 into master will decrease coverage by 71.35%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master   #2106       +/-   ##
==========================================
- Coverage   71.35%      0%   -71.36%     
==========================================
  Files         174     174               
  Lines        5735     189     -5546     
  Branches      503       9      -494     
==========================================
- Hits         4092       0     -4092     
+ Misses       1643     189     -1454

[manuzhang]

The distribute service example is disabled temporarily for which I opened #2107

[manuzhang]

Not sure why code coverage drops to 0% 😞