Installing libxml2-dev libxslt-dev is only needed on TruffleRuby < 21.1

* TruffleRuby >= 21.1 installs nokogiri with the packaged libxml2/libxslt
  like on CRuby by default. See oracle/truffleruby#62

Add TruffleRuby 21.2.0.1

Add Ruby 1.9 on Linux and macOS

* On Windows there are no 64-bit builds of Ruby 1.9.
* Fix floatVersion() for head versions.
* Use floatVersion() in more cases instead of regexps.
* Rely on ~/.gemrc to not install gem docs.

Add TruffleRuby 21.2.0

Add Ruby 2.6.8, 2.7.4 and 3.0.2 on Windows

Remove workflow schedule as it causes the workflow to be disabled in …

…forks

Fix ruby-builder.js - Windows io.mkdirP("D:\\")

Add JRuby 9.2.19.0

Enable sassc test on JRuby on Windows

9.2.18.0 has been released, so this should work now.

Add 2.0.0 on Windows too