Update gemspec files

- Add only the files we need for this library and documentation
- Exclude test suite
- Ignore built gems
- Use Dir instead of system git command to list files

.gitignore

@@ -8,3 +8,4 @@ Gemfile.lock
 .bundle
 bin/
 .idea
+*.gem

net-ldap.gemspec

@@ -21,7 +21,7 @@ Our roadmap for Net::LDAP 1.0 is to gain full <em>client</em> compliance with
 the most recent LDAP RFCs (4510-4519, plutions of 4520-4532).}
   s.email = ["blackhedd@rubyforge.org", "gemiel@gmail.com", "rory.ocon@gmail.com", "kaspar.schiess@absurd.li", "austin@rubyforge.org"]
   s.extra_rdoc_files = ["Contributors.rdoc", "Hacking.rdoc", "History.rdoc", "License.rdoc", "README.rdoc"]
-  s.files = `git ls-files`.split $/
+  s.files = Dir["*.rdoc", "lib/**/*"]
   s.test_files = s.files.grep(%r{^test})
   s.homepage = %q{http://github.com/ruby-ldap/ruby-net-ldap}
   s.rdoc_options = ["--main", "README.rdoc"]
@@ -32,6 +32,6 @@ the most recent LDAP RFCs (4510-4519, plutions of 4520-4532).}
   s.add_development_dependency("flexmock", "~> 1.3")
   s.add_development_dependency("rake", "~> 12.3.3")
   s.add_development_dependency("rubocop", "~> 0.49.0")
-  s.add_development_dependency("test-unit")
-  s.add_development_dependency("byebug") unless RUBY_PLATFORM == "java"
+  s.add_development_dependency("test-unit", "~> 3.3")
+  s.add_development_dependency("byebug", "~> 9.0.6") unless RUBY_PLATFORM == "java"
 end