Add apiversion as a field forced into string type

This should resolve this error in the esworker_cloudtrail
`RequestError: TransportError(400, u'mapper_parsing_exception', u'failed to parse [details.apiversion]')`

mq/plugins/cloudtrail.py

@@ -42,7 +42,8 @@ class message(object):
             'details.requestparameters.disableApiTermination',
             'details.responseelements.findings.service.additionalInfo.unusual',
             'details.responseelements.distribution.distributionConfig.callerReference',
-            'details.requestparameters.logStreamName'
+            'details.requestparameters.logStreamName',
+            'details.apiversion'
         ]
 
     def convert_key_raw_str(self, needle, haystack):