Hex strings are automatically converted to integers

A matched hex-notation string is automatically converted to integers instead of remaining in their original form.

Data: `Process ID: 0x1268`
Grok: `Process ID: +%{DATA:pid}}`
Expected match:
```
[
  {
    "pid": 0x1268
  }
]
```

Actual result:
```
[
  {
    "pid": 4712
  }
]
```
