mounttab: spec should test that fstab options is optional

[domcleal]

The options field in an fstab is optional and has been fixed in Augeas recently. Once a release with this is available, the spec examples to test the provider can be enabled.

Puppet::Type::Mounttab::ProviderAugeas with full file when updating dump should add options first, then dump
  # release of Augeas where options field is optional
  # ./spec/unit/puppet/mounttab_spec.rb:264
Puppet::Type::Mounttab::ProviderAugeas with full file when updating pass should add options and dump first, then pass
  # release of Augeas where options field is optional
  # ./spec/unit/puppet/mounttab_spec.rb:316

[domcleal]

Fixed by using the augeas submodule for access to the latest lens.