Object type spread failing on imported type from other module or libdef (e.g. flow-typed)

`babel-7` branch - I'm looking into this. `found` is in a local libdef.

```javascript
import type {RoutingState} from 'found'

type Props = {
...$Exact,
classes: Object,
children?: Element<*>,
currentUser?: CurrentUser,
t: Function,
width: string,
}
```


```
TypeError: src/App/AppFrame.js: Cannot read property 'key' of undefined
at /Users/kross/projects/ui/node_modules/@alienfast/babel-plugin-flow-react-proptypes/lib/makePropTypesAst.js:154:19
at Array.map (native)
at makeObjectAstForShape (/Users/kross/projects/ui/node_modules/@alienfast/babel-plugin-flow-react-proptypes/lib/makePropTypesAst.js:153:48)
at makePropTypesAstForPropTypesAssignment (/Users/kross/projects/ui/node_modules/@alienfast/babel-plugin-flow-react-proptypes/lib/makePropTypesAst.js:43:12)
at annotate (/Users/kross/projects/ui/node_modules/@alienfast/babel-plugin-flow-react-proptypes/lib/index.js:101:85)
at /Users/kross/projects/ui/node_modules/@alienfast/babel-plugin-flow-react-proptypes/lib/index.js:181:20
at Array.forEach (native)
at PluginPass.ClassDeclaration (/Users/kross/projects/ui/node_modules/@alienfast/babel-plugin-flow-react-proptypes/lib/index.js:178:29)
at newFn (/Users/kross/projects/ui/node_modules/babel-traverse/lib/visitors.js:266:21)
at NodePath._call (/Users/kross/projects/ui/node_modules/babel-traverse/lib/path/context.js:71:18)
```