Add dependency on logger gem

This is required for Ruby 3.5, and warns in Ruby 3.4.

Author: herwinw

xmlrpc.gemspec

@@ -18,6 +18,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.required_ruby_version = ">= 2.3"
 
+  spec.add_dependency "logger"
   spec.add_dependency "rexml"
   spec.add_dependency "webrick"
 end