Allow specifying var decl annots
Allow specifying var decl annots

Summary:
Allow specifying var decl annots so we can construct the following code:

```
const a: number = 1;
```

Reviewed By: mroch

Differential Revision: D22821727

fbshipit-source-id: 20d4bdbd875e49476b622453d9b6a924c0e02210

mroch/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow