update package.json

Adding gulp-filter that enables modification I suggested in the gulpfile.

package.json

@@ -14,6 +14,7 @@
     "font-awesome": "^4.6.3",
     "gulp": "^3.9.1",
     "gulp-clean-css": "^2.0.10",
+    "gulp-filter": "^4.0.0",
     "gulp-header": "^1.8.7",
     "gulp-less": "^3.1.0",
     "gulp-rename": "^1.2.2",