Ensure sslmode=disable is respected

It appears that crystal-pg is not compatible with PostgreSQL instances that do not have SSL support, and it seems to be ignoring the sslmode=disable parameter. This issue is particularly evident with PostgreSQL databases provisioned in Fly.io since they are accessed over an encrypted internal network, and SSL is not supported in such cases (ref).

To illustrate, I was trying to make this seemingly simple script work:

require "db"
require "pg"

DB.connect ENV["DATABASE_URL"] do |cnn|
  p cnn
end

And I got the following trace:

Trace

``` Unhandled exception: (DB::ConnectionRefused) from lib/pg/src/pg/connection.cr:16:9 in 'initialize' from lib/pg/src/pg/connection.cr:7:5 in 'new' from lib/pg/src/pg/driver.cr:3:5 in 'build_connection' from lib/db/src/db.cr:163:5 in 'build_connection' from lib/db/src/db.cr:159:5 in 'build_connection' from lib/db/src/db.cr:142:5 in '__crystal_main' from /usr/share/crystal/src/crystal/main.cr:115:5 in 'main_user_code' from /usr/share/crystal/src/crystal/main.cr:101:7 in 'main' from /usr/share/crystal/src/crystal/main.cr:127:3 in 'main' from /lib/x86_64-linux-gnu/libc.so.6 in '??' from /lib/x86_64-linux-gnu/libc.so.6 in '__libc_start_main' from bin/test in '_start' from ??? Caused by: SSL_connect: I/O error (OpenSSL::SSL::Error) from /usr/share/crystal/src/openssl/ssl/socket.cr:34:11 in 'initialize:context:sync_close' from /usr/share/crystal/src/openssl/ssl/socket.cr:3:5 in 'new:context:sync_close' from lib/pg/src/pq/connection.cr:60:16 in 'negotiate_ssl' from lib/pg/src/pq/connection.cr:40:7 in 'initialize' from lib/pg/src/pq/connection.cr:21:5 in 'new' from lib/pg/src/pg/connection.cr:13:23 in 'initialize' from lib/pg/src/pg/connection.cr:7:5 in 'new' from lib/pg/src/pg/driver.cr:3:5 in 'build_connection' from lib/db/src/db.cr:163:5 in 'build_connection' from lib/db/src/db.cr:159:5 in 'build_connection' from lib/db/src/db.cr:142:5 in '__crystal_main' from /usr/share/crystal/src/crystal/main.cr:115:5 in 'main_user_code' from /usr/share/crystal/src/crystal/main.cr:101:7 in 'main' from /usr/share/crystal/src/crystal/main.cr:127:3 in 'main' from /lib/x86_64-linux-gnu/libc.so.6 in '??' from /lib/x86_64-linux-gnu/libc.so.6 in '__libc_start_main' from bin/test in '_start' from ??? Caused by: SSL_connect: Resource temporarily unavailable (RuntimeError) ```

It should be noted that while I was testing this, the DATABASE_URL environment variable was complying to the following format: postgres://<user>:<pwd>@<host>:<port>/<db>?sslmode=disable.

This seems to indicate that crystal-pg is trying to require an SSL connection when it shouldn't.

In this pull request, I am providing a fairly simple fix to this. Let me know if I am missing something or if this is not the right way to go about this!

will / crystal-pg

Ensure sslmode=disable is respected #268