Don't use a forking server - use threads instead.

I think this may help solve the travis CI build problems--the forked process may be exiting with another status code causing a failed spec run even though no specs failed.

The forked process approach was needed for Patron in the past but that appears to be fixed.

spec/support/vcr_localhost_server.rb

@@ -81,10 +81,7 @@ def concurrently
     end
 
     def should_use_subprocess?
-      # Patron times out when the server is running in a separate thread in the same process,
-      # so use a separate process.
-      # In all other cases, we can use a thread (it's faster!)
-      defined?(Patron)
+      false
     end
 
     def wait_until(timeout, error_message, &block)