stand: liblua: drop default buffer size to 128

[kevans]

Summary

Lua allocates LUAL_BUFFERSIZE buffers on the stack for various string functions (string.format, string.gsub) -- this works out to be somewhat significant and not necessary, based on how we use string operations. Dropping it risks having to allocate per call to format/gsub, but this is not the case for our usage -- we simply stop allocating 8K buffers on the stack when luaL_Buffer is used.