Coverting 3.0 -> 3.1: exclusiveMaximum/minimum doesn't work if minimum/maximum is `0` (zero number)

Converting zero values on minimum or maximum (exclusiveMaximum/exclusiveMinimum) are skipped:

E.g.
```
"FalseyExclusiveMinMax": {
  "properties": {
    "minIsZero": {
      "type": "integer",
      "maximum": 1,
      "minimum": 0,
      "exclusiveMaximum": true,
      "exclusiveMinimum": true
    },
  }
}
```

results in:
```
"exclusiveMinimum": true
```
when it should be `exclusiveMinimum: 0`.