Upgrade devDependencies

Author: jakezatecky

package.json

@@ -48,7 +48,7 @@
     "gulp-eslint": "^4.0.0",
     "gulp-header": "^2.0.5",
     "gulp-mocha": "^5.0.0",
-    "gulp-sass": "^3.0.0",
+    "gulp-sass": "^4.0.1",
     "gulp-scss-lint": "^0.6.1",
     "jsdom": "^11.0.0",
     "mocha": "^5.0.5",