Add base64 to gemfile or gemspec

[UlyssesZh]

/home/ulysses/.local/share/gem/ruby/3.3.0/gems/em-websocket-0.5.3/lib/em-websocket/handshake04.rb:2: warning: base64 was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.4.0. Add base64 to your Gemfile or gemspec. Also contact author of em-websocket-0.5.3 to add base64 into its gemspec.