chore(package): update del to version 5.1.0

Closes #19

Author: greenkeeper[bot]

package.json

@@ -48,7 +48,7 @@
     "browser-cookies": "^1.2.0",
     "chai": "^4.0.0-canary.1",
     "coveralls": "^3.0.3",
-    "del": "^3.0.0",
+    "del": "^5.1.0",
     "eslint": "^4.9.0",
     "eslint-config-airbnb-base": "^12.1.0",
     "eslint-plugin-import": "^2.9.0",