Net::LDAP.new deprecation warning

[tkanov]

When encryption parameter is passed as String to Net::LDAP.new

ldap_options = {
  ...
  encryption: 'ssl',
}
ldap = GitHub::Ldap.new ldap_options

it produces the following deprecation warning
Deprecation warning: please give :encryption option as a Hash to Net::LDAP.new

At present, the encryption value must be a Hash with parameters, which consists of two keys:
method: - :simple_tls or :start_tls
tls_options: - Hash of options for that method

[tkanov]

A PR to fix #99

[tkanov]

up :)