chore(package): update eslint-plugin-unicorn to version 20.0.0

Closes #408

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "eslint-plugin-node": "11.0.0",
     "eslint-plugin-promise": "4.2.1",
     "eslint-plugin-standard": "4.0.1",
-    "eslint-plugin-unicorn": "18.0.1",
+    "eslint-plugin-unicorn": "20.0.0",
     "jest": "22.4.2",
     "npm-merge-driver": "2.3.6",
     "pre-git": "3.17.1",