Modernize gemspec & remove unnecessary files to reduce size

Author: segiddins

rails-footnotes.gemspec

@@ -3,7 +3,6 @@ require_relative "./lib/rails-footnotes/version"
 Gem::Specification.new do |s|
   s.name        = "rails-footnotes"
   s.version     = Footnotes::VERSION
-  s.platform    = Gem::Platform::RUBY
   s.authors     = ["Roman V. Babenko", "José Valim", "Keenan Brock", "Duane Johnson", "Adrien Siami", "André Arko"]
   s.email       = ["[email protected]"]
   s.homepage    = "https://github.com/indirect/rails-footnotes"
@@ -13,7 +12,13 @@ Gem::Specification.new do |s|
   s.add_dependency "rails", "~> 7.0"
   s.required_ruby_version = ">= 3.0"
 
-  s.files         = `git ls-files`.split("\n")
-  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
+  # 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.
+  s.files =
+    IO.popen(["git", "-C", __dir__, "ls-files", "-z", "--", "exe/", "lib/", "*.md", "*.txt", "CHANGELOG", "*LICENSE"], &:read).split("\x0")
+      .reject do |f|
+      (File.expand_path(f) == __FILE__) ||
+        f.start_with?(*%w[bin/ test/ spec/ features/ .git .github appveyor Gemfile Rakefile tasks/])
+    end
   s.require_paths = ["lib"]
 end