Serverpilot now offers both SSL and HTTP/2 support out of the box on their paid plans. Moving forward HTTP/2 is replacing SPDY. As the Serverpilot team mentioned in their blog post:

The HTTP/2 standard evolved from an earlier protocol called SPDY that was developed by Google. After multiple years of development and evolution of the SPDY protocol, as well as feedback from many organizations using SPDY, a new HTTP/2 standard was created that improved further on the SPDY protocol.

With the standardization of HTTP/2, browsers are now removing support for SPDY and only supporting HTTP/2.

If you’re not on their paid plans, you can still install an SSL certificate manually. This article on using Let’s Encrypt with Nginx should point you in the right direction.