Fix logic to select the latest JRuby version

* The maven 'latest' field is unusuable, the order is unpredictable and
  we need to skip old 9000.dev-SNAPSHOT snapshots.
  See jruby/jruby#6713

Author: eregon

find-jruby-head-url-nokogiri.rb

@@ -1,4 +1,5 @@
 require 'open-uri'
+require 'rubygems'
 require 'nokogiri'
 
 base_url = 'https://oss.sonatype.org/content/repositories/snapshots/org/jruby/jruby-dist'
@@ -9,7 +10,9 @@
 STDERR.puts xml
 
 versions = Nokogiri::XML(xml).css('version').map(&:text)
-most_recent = (versions - %w[9000.dev-SNAPSHOT]).last
+
+versions.delete('9000.dev-SNAPSHOT')
+most_recent = versions.max_by { |v| Gem::Version.new(v) }
 
 builds_url = "#{base_url}/#{most_recent}/maven-metadata.xml"
 STDERR.puts builds_url

find-jruby-head-url.rb

@@ -1,4 +1,5 @@
 require 'open-uri'
+require 'rubygems'
 
 module MicroXMLParser
   HEADER = %r{<\?xml\s.+\?>\n}
@@ -65,7 +66,9 @@ def self.rec(xml)
 
 parsed = MicroXMLParser.parse(xml)
 versions = parsed.dig(:metadata, :versioning, :versions).map { |e| e[:version] }
-most_recent = (versions - %w[9000.dev-SNAPSHOT]).last
+
+versions.delete('9000.dev-SNAPSHOT')
+most_recent = versions.max_by { |v| Gem::Version.new(v) }
 
 builds_url = "#{base_url}/#{most_recent}/maven-metadata.xml"
 STDERR.puts builds_url