[rubygems/rubygems] Make rescue clause more specific

This is hiding a real bundler issue as a "network error". It's more
helpful to get a proper bug report, with stack trace and so on.

So stop re-raising errors when evaluating unmarshaled  responses  as
network errors, and only raise Marshal errors when the Marshal format is
invalid, not whenever marshalled gemspecs can't be loaded because that
may hide actual client errors, like missing `YAML` constants.

https://github.com/rubygems/rubygems/commit/05ea907e1c

lib/bundler.rb

@@ -561,7 +561,7 @@ EOF
 
     def load_marshal(data)
       Marshal.load(data)
-    rescue StandardError => e
+    rescue TypeError => e
       raise MarshalError, "#{e.class}: #{e.message}"
     end