If git is present in build env, it causes build failures.

--- a/enumerable-statistics.gemspec
+++ b/enumerable-statistics.gemspec
@@ -19,7 +19,7 @@
   spec.description   = %q{This library provides statistics features for Enumerable}
   spec.homepage      = "https://github.com/mrkn/enumerable-statistics"
 
-  spec.files         = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  spec.files         = Dir.glob("**/*").select {|v| v !~ /^debian/}
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["ext", "lib"]