Don't count buffers and cache in memory graph

I don't think it makes sense to count buffers and cache as "used memory", since after using a computer for a while it's normal for cache and buffers to take all the remaining RAM instead of wasting it. Because of this, the graph most of the times ends up being full and pretty useless.

I personally use the graph to notice when my memory usage starts rising fast so I can do something before swap starts being used and my computer slows down very hard, or, if swap is not enabled, before the kernel starts killing applications. But since this tool is counting buffers and cache as not free memory, even though they can be de-allocated anytime needed without any issues, it makes it useless for me.