GROOVY-6933: Add swap() to List and array.
Collections.swap() returns nothing, but this method returns this object.
First bits of work around quality builds:
   * re-enabled checkstyle
   * generate HTML report
   * CodeNarc, Cobertura disabled
Upgrade to Asciidoctor Gradle plugin 0.7.3
Merge pull request #481 from yukoba/Swap

GROOVY-6933: Add swap() to List and array
Add immutable collections.