Merge pull request #1142 from HansMuller/tabs_typo

Fixed a tabs scrolling typo

packages/flutter/lib/src/material/tabs.dart

@@ -839,7 +839,7 @@ class _TabBarViewState<T> extends PageableListState<TabBarView<T>> implements Ta
       scrollTo(scrollBehavior.updateExtents(contentExtent: 2.0, containerExtent: 1.0, scrollOffset: 0.0));
     } else if (selectedIndex == _tabCount - 1) {
       _updateItems(selectedIndex - 1, selectedIndex);
-      scrollTo(scrollBehavior.updateExtents(contentExtent: 1.0, containerExtent: 1.0, scrollOffset: 1.0));
+      scrollTo(scrollBehavior.updateExtents(contentExtent: 2.0, containerExtent: 1.0, scrollOffset: 1.0));
     } else {
       _updateItems(selectedIndex - 1, selectedIndex, selectedIndex + 1);
       scrollTo(scrollBehavior.updateExtents(contentExtent: 3.0, containerExtent: 1.0, scrollOffset: 1.0));