Disable usage of git in gemspec, preventing gemspec installation.

--- a/faraday.gemspec
+++ b/faraday.gemspec
@@ -18,5 +18,5 @@
 
   spec.add_dependency 'multipart-post', '>= 1.2', '< 3'
 
-  spec.files = `git ls-files -z lib LICENSE.md README.md`.split("\0")
+  spec.files = Dir.glob('{lib}/**/*') + %w(LICENSE.txt README.md)
 end