chore(package): update del to version 5.1.0

Closes #26

Author: greenkeeper[bot]

package.json

@@ -73,7 +73,7 @@
     "core-js": "^2.6.9",
     "css-loader": "^2.1.0",
     "cssnano": "^4.1.8",
-    "del": "^3.0.0",
+    "del": "^5.1.0",
     "fancy-log": "^1.3.3",
     "greenkeeper-lockfile": "^1.15.1",
     "gulp": "3.9.1",