Update prettier to version 2.1.0

Author: depfu[bot]

package.json

@@ -38,7 +38,7 @@
     "eslint-plugin-standard": "^4.0.0",
     "mocha": "^7.0.0",
     "nyc": "^15.0.0",
-    "prettier": "~2.0.2",
+    "prettier": "~2.1.0",
     "unexpected": "^11.12.1"
   },
   "author": "Sune Simonsen",