Update gempsec to require nio4r 2.5.5

This will address the rare edge case of an application using Puma 6 but
a pre-2.5.5 version of nio4r, which will manifest inconsistent
::NIO::Selector.new behavior.

As cited in
puma#3542 (comment), 2.5.5 is
4 years old now, but this bump of the minimum requirement on the puma
side technically shouldn't hurt.

lib/puma/reactor.rb

@@ -24,12 +24,8 @@ def initialize(backend, &block)
       unless valid_backends.include?(backend)
         raise ArgumentError.new("unsupported IO selector backend: #{backend} (available backends: #{valid_backends.join(', ')})")
       end
-      delete_output = NIO::Selector.backends.delete(backend)
-      if delete_output.nil?
-        @selector = ::NIO::Selector.new
-      else
-        @selector = ::NIO::Selector.new(delete_output)
-      end
+
+      @selector = ::NIO::Selector.new(NIO::Selector.backends.delete(backend))
       @input = Queue.new
       @timeouts = []
       @block = block

puma.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |s|
   s.email = ["evan@phx.io"]
   s.executables = ["puma", "pumactl"]
   s.extensions = ["ext/puma_http11/extconf.rb"]
-  s.add_runtime_dependency "nio4r", "~> 2.0"
+  s.add_runtime_dependency "nio4r", "~> 2.5.5"
   if RbConfig::CONFIG['ruby_version'] >= '2.5'
     s.metadata["msys2_mingw_dependencies"] = "openssl"
   end

test/test_reactor.rb

@@ -1,7 +1,7 @@
 require 'puma/reactor'
 require_relative "helper"
 
-class TestReactor < Minitest::Test
+class TestReactor < TimeoutTestCase
   def test_initialization_on_jruby
     skip_unless :jruby
     @reactor = Puma::Reactor.new(:auto) { |c| reactor_wakeup c }