fixes #531

Gulp uses a package called [vinyl-fs](https://github.com/wearefractal/vinyl-fs), which relies on a package called [glob-watcher](https://github.com/wearefractal/glob-watcher), which relies on a package called [gaze](https://github.com/shama/gaze). Versions of gaze later than 0.5.1 cause the problems described in #531. 

glob-watcher is compatible with gaze v0.5.1. If we set gulp to require gaze 0.5.1, glob-watcher will use this version.