"minimum": 0.0 is not set when @Min(0) is used

Consider the following:

```
public class Person {
@Min(0)
private int id;
}
```

when serialized to json schema, will output:

```
{
"type" : "object",
"id" : "urn:jsonschema:xxx:Person",
"properties" : {
"id" : {
"type" : "integer"
}
}
```

instead of:

```
{
"type" : "object",
"id" : "urn:jsonschema:xxx:Person",
"properties" : {
"id" : {
"type" : "integer",
"minimum" : 0.0
}
}
```

everything works fine if we define any other number than 0.

By looking at the ValidationConstraintResolver/AnnotationConstraintResolver, why the minimumValue/maximumValue is always converted to double?

When the type is integer, shoudn't the minimum/maximum value stays to an integer format?
When I look at the following documentation:
http://spacetelescope.github.io/understanding-json-schema/reference/numeric.html
Under range, the integer format is preserved. Should I open different issues for this?

Thank you very much!