Disable SSLv3 for the server connection

Disable SSLv3 for both Net::HTTP and HTTPClient. Committing this as a
quick incident response. Test will be provided tomorrow.
can we reset SET_SSL_OP_NO_SSLv3 for more safety?
Fortunately, td-client-ruby creates http client instance every time when it issues a HTTP request. so, it should be possible to reset SET_SSL_OP_NO_SSLv3 flag at the end of API#get and API#post methods.
I think it is optional because fluent-plugin-td (the major user of td-client-ruby) will use a dedicated thread for uploading. But better to have.