Update grunt-dust-html.js to use dust-helpers if available

The dust-helpers should be used when available.
Have to set  dust.optimizers.format before the template is compiled if it should have any effect.
Merge pull request #6 from kmartinson/master

Setting the whitespace option to true doesn't have any effect, the whitespaces are not preserved.
Merge pull request #5 from ericponto/master

Allow support for the linkedin dust helpers.
bump version
Merge commit '26ab08247d1dbe48936ce8ebf9734526ae456aea'