Explicitly use SSLv3 for post-receive hook

I had the problem that mirrors where not automatically updated. After a lot of debugging of the post-receive hook I found the reason to be the following:

When Redmine runs on mod_passenger with apache2 with SSL on Debian 7 the post-receive hook fails. Apache2's mod_ssl configuration disables SSLv2 for security reasons. Ruby 1.9.3 still tries to connect using SSLv2 and fails to establish the connection. This PR changes the ssl version to SSLv3.