open temp file as binary to suppress LF->CRLF conversion on Windows

This command on Windows currently fails:
```bosh --no-color upload release releases/cf-177.yml```

with error:

```uaa (e95f22b7838e41bde03de3e10ffc5dddbfdfbd9a) FOUND REMOTE
Downloading package uaa (e95f22b7838e41bde03de3e10ffc5dddbfdfbd9a) from blobstore (id=d9c58bd8-6581-4727-8f2d-3a187e99c8e5)...
Blobstore error: sha1 mismatch expected=0ddf3ca5aafba07afee7b9d25d9451347738ef35 actual=67dd8b8e568eeb790acaa123bb6bdcc891ad1c46```


because the file during download is saved using a Ruby API that defaults to a mode that performs LF->CRLF conversion on Windows. With this patch the conversion is suppressed and the command completes successfully.