Using the previous dependency versions, the build always failed during
the documentation tasks; this was due to an incompatibility between
Kotlin and Gradle (see Kotlin/dokka#428).

Update Kotlin to 1.4.30 (not the latest version, but the latest version
available in IDEA). KTLint could not be updated to 0.41.0 because of
some weird behavior with the plugin (sample/Main.kt indentation is
marked as incorrect).

Update the configuration blocks, as well (the `dokka` block is no more).

Without this, if Windows fails then we won't test Mac.

I'm honestly not sure why this is required, since Kotlin files are
supposed to always be UTF-8. Without this, though, the build fails on
Windows due to all special table characters being turned into ???.

Fixes JakeWharton#29.