Export history contained base64 encoded firstDecisionCompletedId

[vancexu]

History exported from UI has base64 encoded value for firstDecisionCompletedId
for example:

[ 
   { 
      "eventId":1,
      "timestamp":1572983709126469187,
      "eventType":"WorkflowExecutionStarted",
      "version":300,
      "taskId":446074314,
      "workflowExecutionStartedEventAttributes":{ 
         "workflowType":{ 
            "name":"PointTierAggregationWorkflow"
         },
         "taskList":{ 
            "name":"fx-worker-lunacore-0"
         },
         "input":"some dummy context g==",
         "executionStartToCloseTimeoutSeconds":864000,
         "taskStartToCloseTimeoutSeconds":10,
         "continuedExecutionRunId":"3f5a7b60-0e8d-4278-9d28-f5173b18f164",
         "originalExecutionRunId":"0de4c876-6592-4eba-b021-8dd3ec8854b3",
         "identity":"",
         "firstExecutionRunId":"bc0034d5-03c1-492e-b353-4a4a3cc4ae2c",
         "attempt":0,
         "prevAutoResetPoints":{ 
            "points":[ 
               { 
                  "binaryChecksum":"51c5b8b69ddba7aa6f967f6af63cbd6c",
                  "runId":"19343c17-a3c2-4cbe-8a15-5154c7cfe5ed",
                  "firstDecisionCompletedId":"AAAAAAAAAAQ=",
                  "createdTimeNano":1562702097534937255,
                  "expiringTimeNano":1564516497557519770,
                  "resettable":true
               },
               { 
                  "binaryChecksum":"277938d0d643a212cb7a152954abc8f3",
                  "runId":"19343c17-a3c2-4cbe-8a15-5154c7cfe5ed",
                  "firstDecisionCompletedId":"AAAAAAAAAAw=",
                  "createdTimeNano":1563306897557479300,
                  "expiringTimeNano":1564516497557519770,
                  "resettable":true
               },
               ......
            ]
         },
         "header":{ 
            "fields":{ 

            }
         }
      }
   },
   { 
      "eventId":2,
      "timestamp":1572983709126505634,
      "eventType":"DecisionTaskScheduled",
      "version":300,
      "taskId":446074315,
      "decisionTaskScheduledEventAttributes":{ 
         "taskList":{ 
            "name":"fx-worker-lunacore-0"
         },
         "startToCloseTimeoutSeconds":10,
         "attempt":0
      }
   },
   ...
]

Using such file directly in reply test will caused error:
cannot unmarshal string into Go struct field ResetPointInfo.firstDecisionCompletedId of type int64

UI exported history should be same as CLI output:
cadence --do domain wf show -w <wid> -r <rid> --output_filename history.json