The existing signature conflicts with one added to JRuby 9.2.9.
Specifically, the new signature in JRuby returns RubyArray, which
causes a compilation error on this line in Nokogiri because it
attempts to use a more general return type.

We would prefer to keep the specific return type in JRuby.

* If we patch JRuby, then 9.2.9 will never be able to compile any
  version of Nokogiri.
* If we patch Nokogiri, all versions of JRuby can compile current
  and future Nokogiri. Versions prior to 9.2.9 will be able to
  compile all existing releases of Nokogiri.

I do not believe the change in 9.2.9 breaks anything at runtime,
since the JVM does not care about this particular return type
mismatch unless someone actually returns a non-RubyArray object.

Fixes sparklemotion#1968