Fix flow errors (#502)

Summary:
We had a brief moment without Flow coverage, where this must have snuck
in. Not sure if there's a better type for `node` given the current
structure, but the rest should be obvious.
Pull Request resolved: https://github.com/facebook/flipper/pull/502

Test Plan: flow

Reviewed By: jknoxville

Differential Revision: D16533248

Pulled By: passy

fbshipit-source-id: 51e493208050e4af531e161fb49eda77fdf2494e

src/plugins/sections/Tree.js

@@ -62,11 +62,13 @@ type TreeData = Array<{
   removed?: boolean,
   updated?: boolean,
   unchanged?: boolean,
+  isSection?: boolean,
+  isDataModel?: boolean,
 }>;
 
 type Props = {
   data: TreeData | SectionComponentHierarchy,
-  nodeClickHandler?: (node, evt) => void,
+  nodeClickHandler?: (node: any, evt: InputEvent) => void,
 };
 
 type State = {