fix "Error: Extra data:" error

When using 1Password 4, it seems that I get this error on some entries:

```
1pass: Error: Extra data: line 1 column 800 - line 1 column 816 (char 800 - 816)
```

I tracked it down to there be extra non-printing characters at the end of the decrypted json data.  This change fixed it for me.