Validate fails incorrectly for integer values

[tylergannon]

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Describe the bug
Validator fails on schema type "integer".

To Reproduce
Make a schema that contains an integer data type and then validate an object using that schema.

Expected behavior
Validation should pass

Additional context

Golang unmarshals all numbers as float64. The type check for data.(int) therefore fails.

What will succeed will be

	case jsonschema.Integer:
		if num, ok := data.(float64); ok {
			if num == float64(int64(num)) {
				return true
			}
		}
		if _, ok := data.(int); ok {
			return true // Just in case other versions of Golang support this
		}

I don't have the time to create a PR at this point so I've just copied your validate.go into my own codebase FTTB.