Make generated netbox-client-ruby.gem file smaller

Actually we don't need all these (other) files to run the gem in a Docker image

Author: n-rodriguez

netbox-client-ruby.gemspec

@@ -21,9 +21,7 @@ Gem::Specification.new do |spec|
     spec.metadata['bug_tracker_uri']   = 'https://github.com/ninech/netbox-client-ruby/issues'
   end
 
-  spec.files = `git ls-files -z`.split("\x0").reject do |f|
-    f.match(%r{^(test|spec|features)/})
-  end
+  spec.files = Dir['README.md', 'LICENSE.txt', 'VERSION', 'lib/**/*.rb']
 
   spec.required_ruby_version = '>= 2.7.0'