Adds a new root project to set Scala version

[fedefernandez]

This PR adds a new root project in order to define the Scala version

Scala formatter has formatted some configuration files, but the only change is:

lazy val root = (project in file("."))
  .settings(buildSettings: _*)
  .aggregate(github4sJVM, github4sJS, scalaz, docs)

Please @juanpedromoreno could you review? Thanks

[codecov-io]

Current coverage is 85.82% (diff: 100%)

Merging #50 into master will not change coverage

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  Lines           402        402          
  Methods         398        398          
  Messages          0          0          
  Branches          3          3          
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  Hits            345        345          
  Misses           57         57          
  Partials          0          0          

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[juanpedromoreno]

LGTM!