getScrollResponder is not a function

When running a snapshot test wit jest on a component using the `SortableListView`, I get following error:

```
node_modules/react-native-sortable-listview/index.js:186
_this3.scrollResponder=_this3.refs.list.getScrollResponder();
^
TypeError: _this3.refs.list.getScrollResponder is not a function
at null._onTimeout (node_modules/react-native-sortable-listview/index.js:186:41)
at Timer.listOnTimeout (timers.js:92:15)
npm ERR! Test failed. See above for more details.

```

When I look into the `refs.list`, indeed the getScrollResponder() doesn't exits.

I run react native 0.42.3
And version 0.2.2 of this module

Is there something special I should do with snapshot tests? I followed the example.

Start by reproducing the snapshot test with React Native 0.42.3 and module version 0.2.2, then inspect node_modules/react-native-sortable-listview/index.js around line 186 and the SortableListView ref. Confirm that the snapshot test completes without the getScrollResponder error and that its expected snapshot remains valid.

Written by the indexing model from the issue text.