add proptypes to app.js

App.js

@@ -1,6 +1,7 @@
 /** @type {AppStorage} */
 import './shim.js'
 import React from 'react'
+import PropTypes from 'prop-types'
 import { Text, ScrollView, StyleSheet } from 'react-native'
 import { DrawerNavigator, SafeAreaView } from 'react-navigation'
 import MainBottomTabs from './MainBottomTabs'
@@ -24,6 +25,12 @@ const CustomDrawerContentComponent = (props) => (
   </ScrollView>
 )
 
+CustomDrawerContentComponent.propTypes = {
+  navigation: PropTypes.shape({
+    navigate: PropTypes.func
+  })
+}
+
 const styles = StyleSheet.create({
   container: {
     marginTop: 20,

package.json

@@ -45,6 +45,7 @@
     "mocha": "^5.0.4",
     "node-libs-react-native": "^1.0.1",
     "process": "^0.11.10",
+    "prop-types": "^15.6.1",
     "react": "16.0.0",
     "react-native": "https://github.com/expo/react-native/archive/sdk-23.0.0.tar.gz",
     "react-native-camera": "^0.12.0",