lua: tune jit feature recommended by agentzh

frameworks/Lua/openresty/nginx.conf

@@ -9,7 +9,7 @@ http {
     resolver 127.0.0.1;
     access_log off;
     lua_package_path 'CWD/?.lua;;';
-    init_by_lua 'require "resty.core" encode = require("cjson").encode mysql = require("resty.mysql")';
+    init_by_lua 'jit.opt.start("minstitch=10"); require "resty.core" encode = require("cjson").encode mysql = require("resty.mysql")';
     server {
         listen       8080;
         location /plaintext {