Litres show up as lowercase `l`

Litres show up as a lowercase `l` which is, to my knowledge, a lot less commonly used than the uppercase `L`, and harder to read in some fonts: ``` > 20 L/s = 20 l/s [FlowRate] ``` Could this be fixed by reversing the order from `l: short, L: short` to `L: short, l: short` here? https://github.com/sharkdp/numbat/blob/7d0365d37f52f6217f7bbcb0243a2a3389e06945/numbat/modules/units/si.nbt#L232