Fix integer casting issues in Mac OSS build
Fix integer casting issues in Mac OSS build

Summary:
We were getting the following error:

```
error: return type 'long long' must match previous return
      type 'long' when lambda expression has unspecified explicit return type
```

Addresses https://github.com/facebook/redex/issues/328.

Reviewed By: minjang

Differential Revision: D8733385

fbshipit-source-id: a893b627aa784ba3e82b2dda6c66ffe9b967882f

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex