chore(package): update del to version 5.1.0

Closes #40

Author: greenkeeper[bot]

package.json

@@ -68,7 +68,7 @@
     "core-js": "^2.6.5",
     "css-loader": "^1.0.1",
     "cssnano": "^4.1.10",
-    "del": "^3.0.0",
+    "del": "^5.1.0",
     "fancy-log": "^1.3.3",
     "gulp": "^3.9.1",
     "gulp-bump": "^3.1.1",