Replaced references to type() function with is_string() for Puppet 3.7.x, which now reserves the "type" keyword for future use.

https://docs.puppetlabs.com/puppet/3.7/reference/lang_reserved.html#reserved-words
Merge pull request #49 from misterdorm/puppet37x

Replaced references to type() function with is_string() for Puppet 3.7.x...