Adding funding_uri & other metadata

For more information:
- rubygems/rubygems#3390
- rubygems/rubygems#3060

ruby_jard.gemspec

@@ -15,11 +15,15 @@ Gem::Specification.new do |spec|
   spec.license       = 'MIT'
   spec.required_ruby_version = Gem::Requirement.new('>= 2.5.0')
 
-  spec.metadata['allowed_push_host'] = 'https://rubygems.org'
-
-  spec.metadata['homepage_uri'] = spec.homepage
-  spec.metadata['source_code_uri'] = 'https://github.com/nguyenquangminh0711/ruby_jard'
-  spec.metadata['changelog_uri'] = 'https://github.com/nguyenquangminh0711/ruby_jard'
+   spec.metadata = {
+    'allowed_push_host' => 'https://rubygems.org',
+    'bug_tracker_uri' => "#{spec.homepage}/issues",
+    'changelog_uri' => "#{spec.homepage}/blob/master/CHANGELOG.md",
+    'documentation_uri' => spec.homepage,
+    'funding_uri' => 'https://ko-fi.com/nguyenquangminh0711',
+    'homepage_uri' => spec.homepage,
+    'source_code_uri' => spec.homepage
+  }
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.