Lock request@<2.81.0

request@2.81.0 breaks Node < 4 compat.

package.json

@@ -68,7 +68,7 @@
     "nan": "^2.3.2",
     "node-gyp": "^3.3.1",
     "npmlog": "^4.0.0",
-    "request": "^2.79.0",
+    "request": "~2.79.0",
     "sass-graph": "^2.2.4",
     "stdout-stream": "^1.4.0",
     "true-case-path": "^1.0.2"