Add recommended metadata to gemspec file

See https://guides.rubygems.org/specification-reference/#metadata

Author: Envek

after_commit_everywhere.gemspec

@@ -28,7 +28,10 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = spec.homepage
   spec.metadata["changelog_uri"] = "https://github.com/Envek/after_commit_everywhere/blob/master/CHANGELOG.md"
+  spec.metadata["bug_tracker_uri"] = "https://github.com/Envek/after_commit_everywhere/issues"
 
   spec.add_dependency "activerecord", ">= 4.2"
   spec.add_dependency "activesupport"