[BUG] validate JSON for 1.3

[jkowalleck]

validation of

{
  "$schema": "http://cyclonedx.org/schema/bom-1.3.schema.json",
  "bomFormat": "CycloneDX",
  "specVersion": "1.3",
...
}

fails with unexpected validation error

+ [
+   {
+     instancePath: '/$schema',
+     keyword: 'enum',
+     message: 'must be equal to one of the allowed values',
+     params: {
+       allowedValues: [
+         'http://cyclonedx.org/schema/bom-1.3.schema.json'
+       ]
+     },
+     schemaPath: '#/properties/%24schema/enum'
+   }
+ ]