Fix BottomTabs documentation

title was renamed to text

docs/docs/layout-types.md

         children: [],
         options: {
           bottomTab: {
-            title: 'Tab 1',
+            text: 'Tab 1',
             icon: require('../images/one.png')
           }
         }
         name: 'secondTabScreen',
         options: {
           bottomTab: {
-            title: 'Tab 2',
+            text: 'Tab 2',
             icon: require('../images/two.png')
           }
         }

docs/docs/top-level-api.md

           }],
           options: {
             bottomTab: {
-              title: 'Tab 1',
+              text: 'Tab 1',
               icon: require('../images/one.png'),
               testID: 'FIRST_TAB_BAR_BUTTON'
             }
           },
           options: {
             bottomTab: {
-              title: 'Tab 2',
+              text: 'Tab 2',
               icon: require('../images/two.png'),
               testID: 'SECOND_TAB_BAR_BUTTON'
             }