Pin node-sass to satisfy upstream dependency

[jimhotchkin-wf]

Code Review

Ultimate Problem

An upstream dependency of wGulp was itself pulling in a beta version of node-sass which was causing errors in some projects when they attempted to run gulp sass.

Proposed Solution

Add node-sass: 3.3.0 to wGulp's dependencies, which satisfies the upstream dependency and prevents the beta version from being included in the dependency tree.

[jimhotchkin-wf]

@maxwellpeterson-wf @trentgrover-wf @evanweible-wf @dustinlessard-wf

Just a suggestion, based on our experiences. Thanks!

[trentgrover-wf]

closing as duplicate of https://github.com/Workiva/wGulp/pull/159/