lua: update to 5.3.6
    
    This release contains some minor bugfixes; notably:
    - 2x minor Makefile fixes (not used in base)
    - Long brackets with a huge number of '=' overflow some internal buffer
      arithmetic.
    - Joining an upvalue with itself can cause a use-after-free crash.
    
    See here for examples: http://www.lua.org/bugs.html#5.3.5