Add missing specs for `Ronin::CLI::Commands::New::*` classes

[postmodern]

Add missing specs for the additional Ronin::CLI::Commands::New::* command alias classes. At a bare minimum we must test that the command_name matches the file name.

• spec/cli/commands/new/dns_listener_spec.rb
• spec/cli/commands/new/exploit_spec.rb
• spec/cli/commands/new/http_listener_spec.rb
• spec/cli/commands/new/nokogiri_spec.rb
• spec/cli/commands/new/payload_spec.rb
• spec/cli/commands/new/web_app_spec.rb
• spec/cli/commands/new/web_server_spec.rb
• spec/cli/commands/new/web_spider_spec.rb

[postmodern]

See ea0e6bb as an example for what the spec files need to look like.