Update node-sass to 2.1.1

[waldher]

In order to resolve the issue with sass/node-sass#653, node-sass needs to be upgraded to at least 2.0.1, so I'm upgrading to the current version of 2.1.1.

Running 'cake test' after upgrading node-sass was successful:

`--> cake test

> docpad-plugin-nodesass@2.5.1 test /tmp/docpad-plugin-nodesass
> node ./out/sass.test.js

nodesass plugin
nodesass plugin ➞  create
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nodesass plugin ➞  create ✔   
nodesass plugin ➞  load plugin nodesass
nodesass plugin ➞  load plugin nodesass ✔   
nodesass plugin ➞  generate
nodesass plugin ➞  generate ➞  action
OK

[barlock]

The api from 1.2.3 updated in 2.x.x so the plugin requires some work to do the update. The current master branch doesn't run tests like its supposed to. I've made a pull request to update the base files to make the tests run again and I should have another pull request based on those files to update to 2.1.1 by end of day