The malt extract will have some minerals from the mash it was made from. How much is the question?
You can add a little CaCl2 if you want. Yeast benefit from some calcium. A little energizer is not a bad idea either, as it will have trace minerals.
Hmmm, what is the pH optimum for yeast growth? Something around 5.2-5.5 is good for the mash, as you need to get it working in a range for the enzymes. You are not mashing here, just trying to grow yeast. A quick search says 4-4.5 is good for growth. Dr. Tom, any wisdom?