PUP-2745 Forge malformed dependency fix

Prior to this commit a malformed name in the dependencies for a downloaded forge
module dependency would cause the PMT to fail unexpectedly.
This commit causes the PMT to ignore malformed dependencies.

Depends on https://github.com/puppetlabs/puppet/pull/2827
You can do away with this entire conditional if you do something like this before the map:

```ruby
data = @data.dup.merge('dependencies' => @data['dependencies'].to_a)
```

(Obviously, change the key lookups to be against `data` instead...)