temporarily revert root build.gradle back to groovy

[shashachu]

The publish task is not working and I'm not familiar enough with the Kotlin DSL to immediately debug.

[Goooler]

Could you please paste the log here? @shashachu

[Goooler]

I've tested cdc39b1 by running ./gradlew githubRelease, error:

Could not determine the dependencies of task ':githubRelease'.
> Cannot convert () -> org.gradle.api.Task to a task.
  The following types/formats are supported:
    - A String or CharSequence task name or path
    - A Task instance
    - A TaskReference instance
    - A Buildable instance
    - A TaskDependency instance
    - A Provider that represents a task output
    - A Provider instance that returns any of these types
    - A Closure instance that returns any of these types
    - A Callable instance that returns any of these types
    - An Iterable, Collection, Map or array instance that contains any of these types

This should be fixed in #1663.