Special characters break encrypt/decrypt

Having certain special characters in the fields causes them to be printed wrongly after encrypting and decrypting.

With
```json
{ "_public_key": "...", "test": "aaa<bbb>ccc^ddd~eee&fff" }
```
and after
```bash
ejson encrypt test.ejson
ejson decrypt test.ejson
```
I get back `aaa\u003cbbb\u003eccc^ddd~eee\u0026fff` as secret.