Merge pull request #34 from pzatorski/feature/back-button-accessibility

change accessibilityLabel for HeaderBackButton - Fix iOS voiceover

src/views/Header/HeaderBackButton.js

@@ -111,7 +111,7 @@ class HeaderBackButton extends React.PureComponent {
       <TouchableItem
         accessible
         accessibilityComponentType="button"
-        accessibilityLabel={title}
+        accessibilityLabel={title ? `${title}, back` : 'Go back'}
         accessibilityTraits="button"
         testID="header-back"
         delayPressIn={0}