added json parsing heroku filter

lib/plugins/output-filter/heroku-format.js

@@ -1,20 +1,13 @@
-function jsonParse (text) {
-  try {
-    return JSON.parse(text)
-  } catch (err) {
-    return null
-  }
-}
-
 function parseHerokuMessage (data, context) {
   if (data) {
-    data._type = context.sourceName.replace('_' + context.index, '')
-    data.logSource = ('' + data.logSource).replace('_' + context.index, '')
-    if (!data['@timestamp']) {
-      data['@timestamp'] = new Date()
-    }
-    if (data.message) {
-      data.json = jsonParse(data.message)
+    const json = data.json
+    const message = data.message
+    delete data.json
+    delete data.message
+    return {
+      message,
+      ...json,
+      ...data
     }
   }
   return data
@@ -23,18 +16,8 @@ function parseHerokuMessage (data, context) {
 module.exports = function (context, config, eventEmitter, log, callback) {
   try {
     const parsedLog = parseHerokuMessage(log, context)
-    const json = parsedLog.json
-    const message = parsedLog.message
-    delete parsedLog.json
-    delete parsedLog.message
-
-    const structuredLog = {
-      message,
-      ...json,
-      ...parsedLog
-    }
 
-    return callback(null, structuredLog)
+    return callback(null, parsedLog)
   } catch (err) {
     console.error(err)
     return callback(null, log)