If operating on a env variable make sure its there

Fix booting the app without OSEM_SMTP_AUTHENTICATION set

config/environments/production.rb

@@ -76,7 +76,7 @@ Osem::Application.configure do
     port:                 ENV['OSEM_SMTP_PORT'],
     user_name:            ENV['OSEM_SMTP_USERNAME'],
     password:             ENV['OSEM_SMTP_PASSWORD'],
-    authentication:       ENV['OSEM_SMTP_AUTHENTICATION'].to_sym,
+    authentication:       ENV['OSEM_SMTP_AUTHENTICATION'].try(:to_sym),
     domain:		  ENV['OSEM_SMTP_DOMAIN'],
     enable_starttls_auto: true
   }