Always use Bundler 1 for JRuby 9.1.x

Author: eregon

dist/index.js

@@ -215,12 +215,15 @@ async function installBundler(bundlerVersionInput, lockFile, platform, rubyPrefi
     throw new Error(`Cannot parse bundler input: ${bundlerVersion}`)
   }
 
-  if (rubyVersion.match(/^2\.[12]/)) {
+  if (engine === 'ruby' && rubyVersion.match(/^2\.[12]/)) {
     console.log('Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby <= 2.2')
     bundlerVersion = '1'
-  } else if (rubyVersion.startsWith('2.3')) {
+  } else if (engine === 'ruby' && rubyVersion.startsWith('2.3')) {
     console.log('Ruby 2.3 has a bug with Bundler 2 (https://github.com/rubygems/rubygems/issues/3570), using Bundler 1 instead on Ruby 2.3')
     bundlerVersion = '1'
+  } else if (engine === 'jruby' && rubyVersion.startsWith('9.1.')) { // JRuby 9.1 targets Ruby 2.3, treat it the same
+    console.log('JRuby 9.1 has a bug with Bundler 2 (https://github.com/ruby/setup-ruby/issues/108), using Bundler 1 instead on JRuby 9.1')
+    bundlerVersion = '1'
   }
 
   if ((engine === 'ruby' || engine === 'truffleruby') && common.isHeadVersion(rubyVersion) && bundlerVersion === '2') {