Puma does not load a CA when verification mode is set to :peer #1222

Steps to reproduce

1. Configure Puma to accept SSL connections:

key =  File.expand_path "./certs/my_key.key"
cert = File.expand_path "./certs/my_cert.crt"
ca = File.expand_path "./certs/my_ca.crt"

ssl_bind "0.0.0.0", 9292, :ca => ca, :cert => cert, :key => key, :verify_mode => :peer

2. Start Puma, and get the following:

 starting in single mode...
* Version 3.6.2 (ruby 2.3.1-p112), codename: Sleepy Sunday Serenity
* Min threads: 5, max threads: 5
* Environment: production
ERROR: Please specify the SSL ca via 'ca='

Expected behavior

Puma should just start and accept TLS connections.

Actual behavior

Puma exits 1, requesting a CA be specified.

Why it's happening

If mode is set to verify a peer, it requests a CA:

However, the ssl bind method will not attach a CA param to the URL it generates:
https://github.com/puma/puma/blob/master/lib/puma/dsl.rb#L273

If this is a bug and not just me being dumb/wrong, I have no problem submitting a PR to fix it.

System configuration

Ruby version: ruby 2.3.1p112 (2016-04-26 revision 54768)
Rails version: rails (5.0.1)