Update ssmtp.conf.erb

Add auth lines only if options are set. Otherwise mails cannot be sent without authentication.
Merge pull request #13 from twinkler/patch-1

Add auth only when `node['ssmtp']['auth_username']` attribute is set. Otherwise mails cannot be sent without authentication.
update CHANGELOG
Update default.rb

[CHANGE] better way of unsetting a default attribute;
[CHANGE] cleaner way of disabling and enabling auth;
[ADD] notice on readme about auth disabling; [CHANGE] rubocop compliance;
[ADD] rubocop settings; [CHANGE] readme formatting;
Merge pull request #14 from brtz/master

Added ssmtp.auth_enabled (default true) and a bit of cleanup
Moves config file permissions to attributes
Merge pull request #15 from hufman/config_permissions

Moves config file permissions to attributes
#16 Update yum dependencies
#17 Modernize cookbook with latest development tools
Update .travis.yml
Updated README with platforms
Update CHANGELOG to reflect actual releases
Added bats integration test for working sendmail

Looks like bats runs as root via test-kitchen, so this only tests email
sent by root
Added mailtrap to test mail sendability
Adding fedora test kitchen box
Configure without TLS for test-kitchen since mailtrap does not support that
Use /sbin/ssmtp instead of sendmail for cross-platform compatibility

Install pre-release mailtrap gem if 0.2.3 is not found on rubygems

Wait max of 5 seconds for mailtrap to be ready