chore(package): update del to version 5.1.0

Closes #70

Author: greenkeeper[bot]

package.json

@@ -70,7 +70,7 @@
     "core-js": "2.5.7",
     "css-loader": "^1.0.0",
     "cssnano": "^4.1.10",
-    "del": "3.0.0",
+    "del": "5.1.0",
     "gulp": "3.9.1",
     "gulp-bump": "3.1.1",
     "gulp-conventional-changelog": "^2.0.10",