use react prop-types module

src/renderer/components/heading.js

@@ -1,11 +1,12 @@
 const React = require('react')
+const PropTypes = require('prop-types')
 
 const colors = require('material-ui/styles/colors')
 
 class Heading extends React.Component {
   static get propTypes () {
     return {
-      level: React.PropTypes.number
+      level: PropTypes.number
     }
   }
 

src/renderer/components/path-selector.js

@@ -1,6 +1,7 @@
 const colors = require('material-ui/styles/colors')
 const electron = require('electron')
 const React = require('react')
+const PropTypes = require('prop-types')
 
 const remote = electron.remote
 
@@ -11,15 +12,15 @@ const TextField = require('material-ui/TextField').default
 // Uses the system Open File dialog.
 // You can't edit the text field directly.
 class PathSelector extends React.Component {
-  static get propTypes () {
+  static propTypes () {
     return {
-      className: React.PropTypes.string,
-      dialog: React.PropTypes.object,
-      displayValue: React.PropTypes.string,
-      id: React.PropTypes.string,
-      onChange: React.PropTypes.func,
-      title: React.PropTypes.string.isRequired,
-      value: React.PropTypes.string
+      className: PropTypes.string,
+      dialog: PropTypes.object,
+      displayValue: PropTypes.string,
+      id: PropTypes.string,
+      onChange: PropTypes.func,
+      title: PropTypes.string.isRequired,
+      value: PropTypes.string
     }
   }
 
@@ -64,7 +65,8 @@ class PathSelector extends React.Component {
     const textFieldStyle = {
       flex: '1'
     }
-    const text = this.props.displayValue || this.props.value
+
+    const text = this.props.displayValue || this.props.value || ''
     const buttonStyle = {
       marginLeft: 10
     }

src/renderer/components/show-more.js

@@ -1,13 +1,14 @@
 const React = require('react')
+const PropTypes = require('prop-types')
 
 const RaisedButton = require('material-ui/RaisedButton').default
 
 class ShowMore extends React.Component {
   static get propTypes () {
     return {
-      defaultExpanded: React.PropTypes.bool,
-      hideLabel: React.PropTypes.string,
-      showLabel: React.PropTypes.string
+      defaultExpanded: PropTypes.bool,
+      hideLabel: PropTypes.string,
+      showLabel: PropTypes.string
     }
   }
 

src/renderer/pages/preferences-page.js

@@ -1,5 +1,6 @@
 const path = require('path')
 const React = require('react')
+const PropTypes = require('prop-types')
 
 const colors = require('material-ui/styles/colors')
 const Checkbox = require('material-ui/Checkbox').default
@@ -238,7 +239,7 @@ class PreferencesPage extends React.Component {
 class PreferencesSection extends React.Component {
   static get propTypes () {
     return {
-      title: React.PropTypes.string
+      title: PropTypes.string
     }
   }