Update typescript-eslint monorepo to v2.21.0

Author: renovate-bot

package-lock.json

@@ -33,8 +33,8 @@
   "license": "MIT",
   "devDependencies": {
     "@types/debug": "4.1.5",
-    "@typescript-eslint/eslint-plugin": "2.19.2",
-    "@typescript-eslint/parser": "2.19.2",
+    "@typescript-eslint/eslint-plugin": "2.21.0",
+    "@typescript-eslint/parser": "2.21.0",
     "babel-cli": "6.26.0",
     "babel-preset-env": "1.7.0",
     "eslint-config-xo-typescript": "0.24.1",