title: Json schema fails to validate a correct value from a enum property
body: <p>I have the following schema and json, the json schema validation is failing on the log property as it could not find value "yes" on the instance. The same thing passes in the validator tool <a href="https://www.jsonschemavalidator.net/" rel="nofollow noreferrer">https://www.jsonschemavalidator.net/</a> but not in my code. I don't know what is going on</p>
  
  <p>[u'yes'] is not one of ['no', 'yes']</p>
  
  <p>Failed validating 'enum' in schema['properties']['systems']['items']['properties']['log']:
      {'enum': ['no', 'yes']}</p>
  
  <p>On instance['systems'][0]['log']:
      [u'yes']</p>
  
  <p>Schema</p>
  
  <pre><code>{
       "signatures": {
              "type": "array",
              "items": {
                  "type": "object",
                  "properties": {
                    "id": {
                      "type": "string"
                    },
                    "name": {
                      "type": "string"
                    },
                    "description": {
                      "type": "string"
                    },                  
                    "log": {
                      "enum": ["no", "yes"]
                    }                  
                  },
                  "additionalProperties": false
              } 
            }
  }
  </code></pre>
  
  <p>JSON</p>
  
  <pre><code>{
      "signatures": [
          {                       
              "description": "Protocol",             
              "name": "attempt_1",            
              "log": [
                  "yes"
              ],             
              "id": "1550",             
          }
        ]
   }
  </code></pre>