Workaround the segfault that occurs when used with fsevents

fsevents@0.3.8 introduces a segfault that manifests when used with
node-sass. fsevents is widely popular. As a mitigation we've added
fsevents@0.3.7 as an optionalDependency.The intention here is the
prevent users install node-sass@3.3.x and fsevents@0.3.8 by using
npm's deduping behaviour.

package.json

@@ -61,6 +61,9 @@
     "request": "^2.61.0",
     "sass-graph": "^2.0.1"
   },
+  "optionalDependencies": {
+    "fsevents": "0.3.7"
+  },
   "devDependencies": {
     "coveralls": "^2.11.4",
     "cross-spawn": "^2.0.0",