workaround for https://github.com/sass/node-sass/issues/337

i was getting the following until i followed some hints in this thread: https://github.com/sass/node-sass/issues/337

```
warlock-scratch-2 $ warlock

Starting tasks: default
Starting task: flow::templates-to-build
Starting task: flow::coffee-to-build
Starting task: flow::sass-to-build
Starting task: flow::assets-to-build
Starting task: clean::styles-to-build
Starting task: flow::vendor-styles-to-build
[vendor-styles-to-build] Got empty globbing pattern. Skipping flow.
Starting task: flow::styles-to-build
Starting task: clean::scripts-to-build
Starting task: flow::vendor-scripts-to-build
Starting task: flow::scripts-to-build
Starting task: clean::html-to-build
Starting task: clean::scripts-to-compile
Starting task: flow::assets-to-compile
Starting task: clean::styles-to-compile
Starting task: clean::html-to-compile
Assertion failed: (val->IsString()), function _NanGetExternalParts, file ../node_modules/nan/nan.h, line 1725.
Abort trap: 6
```