Don't use git in gemspec

"git ls-files" should be avoided in the gemspec file

simple_state_machine.gemspec

@@ -11,11 +11,9 @@ Gem::Specification.new do |s|
   s.email            = ["FIX@example.com"]
   s.homepage         = %q{http://github.com/mdh/ssm}
   s.extra_rdoc_files = ["LICENSE","README.rdoc"]
-  s.files            = `git ls-files`.split("\n")
-  s.executables      = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
+  s.files            = Dir.glob("lib/**/*") + %w[Changelog.rdoc LICENSE README.rdoc]
   s.rdoc_options     = ["--charset=UTF-8"]
   s.require_paths    = ["lib"]
   s.summary          = %q{A simple DSL to decorate existing methods with logic that guards state transitions.}
-  s.test_files       = `git ls-files -- {test,spec,features}/*`.split("\n")
 end