Objecct -> Object

Sorry, my mistake.
Merge pull request #479 from yukoba/patch-3

Objecct -> Object
Documentation about running one unit test

It is written here
https://github.com/groovy/groovy-core/blob/master/gradle/test.gradle#L66
but I think it is worth writing it on README.adoc.
Merge pull request #480 from yukoba/patch-4

Documentation about running one unit test
First bits of work around quality builds:
   * re-enabled checkstyle
   * generate HTML report
   * CodeNarc, Cobertura disabled