When query is number but property is string convert back to string

* Collection guests setup with a string property token 
 * token is used to store a randomly generated alpha-numeric string
* Query using http GET against deployd:

```
curl -XGET 'http://localhost:3000/guests?token=989394'
```

ACTUAL: prior to this patch, would not return any result 

EXPECTED: query parameter (auto-converted to number) should be treated as string since property is string

This caused a rare bug in our system since numeric-only strings of length 6 would only occur once every 1/((10/36)^6)=~2176 token generation.

Fix and tests attached.