use nginx variable to get magick (#20)

* use nginx variable to get magick

* remove comments

prod/upload/combine.lua

@@ -13,14 +13,13 @@ local origin = {}
 for i = 1, len do
     origin[i] = file_dir .. "/" .. data[i] .. " "
 end
--- linux
-local magick = "/usr/local/ImageMagick/bin/magick"
-local tmp = io.open(magick,"r")
-if tmp == nil then
-    -- mac os
-    magick = "/usr/local/bin/magick"
-else
-    io.close(tmp)
+-- 从 nginx 变量取
+local magick = ngx.var.magick
+
+if not magick then
+    ngx.status = 500
+    ngx.say("image magick not found.")
+    return
 end
 
 local result, _, code = os.execute(magick .. " convert -append " .. table.concat(origin, " ") .. " " .. combined)