Reduce gem size by excluding test files (#569)

This pull request updates the *.gemspec file to optimize the gem package size and structure

$ gem build -o before.tar.gz

$ git switch reduce-gem-size

$ gem build -o after.tar.gz

$ du -sh before.tar.gz after.tar.gz
 108K 	before
 76K 	after

Author: yuri-zubov

Rakefile

@@ -22,14 +22,9 @@ TEXT
 PKG_FILES = FileList[
     "data/**/*",
     "lib/**/*.rb",
-    "spec/**/*.rb",
-    "tasks/**/*.rake",
-    "addressable.gemspec",
     "CHANGELOG.md",
-    "Gemfile",
     "LICENSE.txt",
     "README.md",
-    "Rakefile",
 ]
 
 task :default => "spec"

addressable.gemspec

@@ -13,7 +13,7 @@ Gem::Specification.new do |s|
   s.description = "Addressable is an alternative implementation to the URI implementation that is\npart of Ruby's standard library. It is flexible, offers heuristic parsing, and\nadditionally provides extensive support for IRIs and URI templates.\n".freeze
   s.email = "bob@sporkmonger.com".freeze
   s.extra_rdoc_files = ["README.md".freeze]
-  s.files = ["CHANGELOG.md".freeze, "Gemfile".freeze, "LICENSE.txt".freeze, "README.md".freeze, "Rakefile".freeze, "addressable.gemspec".freeze, "lib/addressable.rb".freeze, "lib/addressable/idna.rb".freeze, "lib/addressable/idna/native.rb".freeze, "lib/addressable/idna/pure.rb".freeze, "lib/addressable/template.rb".freeze, "lib/addressable/uri.rb".freeze, "lib/addressable/version.rb".freeze, "spec/addressable/idna_spec.rb".freeze, "spec/addressable/net_http_compat_spec.rb".freeze, "spec/addressable/security_spec.rb".freeze, "spec/addressable/template_spec.rb".freeze, "spec/addressable/uri_spec.rb".freeze, "spec/spec_helper.rb".freeze, "tasks/clobber.rake".freeze, "tasks/gem.rake".freeze, "tasks/git.rake".freeze, "tasks/metrics.rake".freeze, "tasks/profile.rake".freeze, "tasks/rspec.rake".freeze, "tasks/yard.rake".freeze]
+  s.files = ["CHANGELOG.md".freeze, "LICENSE.txt".freeze, "README.md".freeze, "lib/addressable.rb".freeze, "lib/addressable/idna.rb".freeze, "lib/addressable/idna/native.rb".freeze, "lib/addressable/idna/pure.rb".freeze, "lib/addressable/template.rb".freeze, "lib/addressable/uri.rb".freeze, "lib/addressable/version.rb".freeze]
   s.homepage = "https://github.com/sporkmonger/addressable".freeze
   s.licenses = ["Apache-2.0".freeze]
   s.rdoc_options = ["--main".freeze, "README.md".freeze]