reorg modules

scripts/upload_audio.lua

@@ -2,10 +2,7 @@ package.path = package.path .. ';<SCRIPT_PATH>/?.lua';
 local cjson = require "cjson"
 local http = require "resty.http"
 local create_task = require "lib.create_task"
-local TaskTypes = {
-    NOOP = 'NOOP',
-    CONVERT_AUDIO_FILE = "CONVERT_AUDIO_FILE"
-}
+local TaskTypes = require 'lib.task_type'
 
 local httpc = http.new()
 ngx.req.read_body()