remove git dependency from generating gemspec file. causes errors whe…

…n vendoring this gem in other projects

airbrake.gemspec

@@ -8,9 +8,9 @@ Gem::Specification.new do |s|
   s.summary     = %q{Send your application errors to our hosted service and reclaim your inbox.}
 
   s.require_paths = ["lib"]
-  s.files         = `git ls-files`.split("\n")
-  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
-
+  s.files         = Dir.glob("**/*")
+  s.test_files    = Dir.glob("{test,spec,features}/*")
+  
   s.add_runtime_dependency("builder")
   s.add_runtime_dependency("activesupport")