fix(types): Fix bad classnames usage

.flowconfig

@@ -9,6 +9,7 @@
 index.js
 
 [libs]
+interfaces/
 
 [options]
 suppress_comment=\\(.\\|\n\\)*\\s*\\$FlowFixMe.*

interfaces/classnames.js

@@ -0,0 +1,15 @@
+// flow-typed signature: 3fba12a77525f37b0492c8dab3e04f0e
+// flow-typed version: 94e9f7e0a4/classnames_v2.x.x/flow_>=v0.28.x
+
+type $npm$classnames$Classes =
+  string |
+  {[className: string]: ?boolean } |
+  Array<string> |
+  void |
+  null
+
+declare module 'classnames' {
+  declare function exports(
+    ...classes: Array<$npm$classnames$Classes>
+  ): string;
+}

lib/GridItem.jsx

@@ -363,9 +363,9 @@ export default class GridItem extends React.Component {
     let newChild = React.cloneElement(child, {
       className: classNames('react-grid-item', child.props.className, this.props.className, {
         static: this.props.static,
-        resizing: this.state.resizing,
+        resizing: Boolean(this.state.resizing),
         'react-draggable': isDraggable,
-        'react-draggable-dragging': this.state.dragging,
+        'react-draggable-dragging': Boolean(this.state.dragging),
         cssTransforms: useCSSTransforms
       }),
       // We can set the width and height on the child, but unfortunately we can't set the position.