The default "puma_bind" setting was reintroduced in capistrano3-puma 6.2.0
as "unix://.../tmp/sockets/puma.sock". We no longer need to define it
explicitly in deploy.rb.
NOTE: Although the official capistrano3-puma README still states
that "puma_bind" must be explicitly set after upgrading to v6,
this is no longer true since version 6.2.0. The default value
("unix://.../tmp/sockets/puma.sock") has been restored.