Fixed "json: error calling MarshalJSON for type json.RawMessage"

When I try:
``` go
out, err := SearchRequest(true, "github", "", qry, "", 0)
if err != nil {
  t.Error(err)
}

_, err = json.Marshal(out.Hits.Hits)
```

I receive:
```
--- FAIL: TestSearchResultToJSON (0.01 seconds)
  search_test.go:48: json: error calling MarshalJSON for type json.RawMessage: unexpected end of JSON input
FAIL
exit status 1
```


My commit fix it!