chore(package): update @types/jest to version 21.1.0

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
   },
   "devDependencies": {
     "@reactivex/rxjs": "^5.4.3",
-    "@types/jest": "^20.0.2",
+    "@types/jest": "^21.1.0",
     "@types/node": "^8.0.0",
     "@types/react": "^16.0.5",
     "browserify": "^14.4.0",