Fix automatic bundler installation on JRuby 9.2

bundler.js

@@ -120,13 +120,14 @@ export async function installBundler(bundlerVersionInput, rubygemsInputSet, lock
     }
   }
 
-  // Use Bundler 2.3 when we use Ruby 2.3.2-2.5
+  const targetRubyVersion = common.targetRubyVersion(engine, rubyVersion)
+  // Use Bundler 2.3 when we use Ruby 2.3.2 - 2.5
   // Use Bundler 2.4 when we use Ruby 2.6-2.7
   if (bundlerVersion == '2') {
-    if (engine === 'ruby' && floatVersion <= 2.5) {
-      console.log('Ruby 2.3.2-2.5 only works with Bundler 2.3')
+    if (targetRubyVersion <= 2.5) { // < 2.3.2 already handled above
+      console.log('Ruby 2.3.2 - 2.5 only works with Bundler 2.3')
       bundlerVersion = '2.3'
-    } else if (engine === 'ruby' && floatVersion <= 2.7) {
+    } else if (targetRubyVersion <= 2.7) {
       console.log('Ruby 2.6-2.7 only works with Bundler 2.4')
       bundlerVersion = '2.4'
     }

common.js

@@ -95,6 +95,23 @@ export function isBundler2dot2Default(engine, rubyVersion) {
   }
 }
 
+export function targetRubyVersion(engine, rubyVersion) {
+  const version = floatVersion(rubyVersion)
+  if (engine === 'ruby') {
+    return version
+  } else if (engine === 'jruby') {
+    if (version === 9.1) {
+      return 2.3
+    } else if (version === 9.2) {
+      return 2.5
+    } else if (version === 9.3) {
+      return 2.6
+    }
+  }
+
+  return 9.9 // unknown, assume recent
+}
+
 export function floatVersion(rubyVersion) {
   const match = rubyVersion.match(/^\d+\.\d+/)
   if (match) {