Fix type errors as react types are included in react-native (#95)

Author: Alexander Jarvis

template/package.json

@@ -17,8 +17,7 @@
     "@babel/runtime": "^7.6.2",
     "@react-native-community/eslint-config": "^0.0.5",
     "@types/jest": "^24.0.18",
-    "@types/react": "16.9.0",
-    "@types/react-native": "^0.60.17",
+    "@types/react-native": "^0.60.21",
     "@types/react-test-renderer": "16.9.0",
     "babel-jest": "^24.9.0",
     "jest": "^24.9.0",