Lua binding compatibility for lua 5.3+

1. `luaL_checkint` is replaced by `luaL_checkinteger` and is removed from lua 5.3
2. `lua_isinteger` is already defined in lua 5.3+
3. `else if (isprint(ch))` in `upb/bindings/lua/upbc.cc` is UB when ch is negative, and will crash when compiled by MSVC.