make sure to only try to read files from tar object - closes #31

this fix the problem with some modules that include PaxHeaders
and cause a unexpected token when reading the tar file.

Author: Danilo Sousa

lib/puppet_forge_server/utils/archiver.rb

@@ -24,7 +24,7 @@ def read_from_archive(archive, name_regex)
       tar.rewind
       files = {}
       tar.each do |obj|
-        files[obj.full_name] = obj.read if obj.full_name =~ name_regex
+        files[obj.full_name] = obj.read if obj.file? && obj.full_name =~ name_regex
       end
       return files unless files.empty?
       raise "Given name #{name_regex} not found in #{archive}"