Add prop type checking

package.json

@@ -12,5 +12,8 @@
     "build": "react-scripts build",
     "test": "react-scripts test --env=jsdom",
     "eject": "react-scripts eject"
+  },
+  "devDependencies": {
+    "prop-types": "^15.6.2"
   }
-}
+}

src/App.js

@@ -2,6 +2,7 @@ import React, { Component } from 'react';
 import logo from './logo.svg';
 import './App.css';
 import FeedbackForm from './components/FeedbackForm';
+import PropTypes from 'prop-types';
 
 class App extends Component {
   render() {
@@ -17,4 +18,8 @@ class App extends Component {
   }
 }
 
+App.propTypes = {
+  env: PropTypes.object.isRequired
+};
+
 export default App;

src/components/FeedbackForm.js

@@ -1,3 +1,4 @@
+import PropTypes from 'prop-types';
 import React, { Component } from 'react';
 
 export default class FeedbackForm extends Component {
@@ -83,3 +84,7 @@ export default class FeedbackForm extends Component {
     );
   }
 }
+
+FeedbackForm.propTypes = {
+  env: PropTypes.object.isRequired
+};