Fix -H and -L rolls

[luccasclezar]

I noticed this package is not maintained anymore, but I'm using it now so I thought to contribute by fixing these errors. 🙂

• More than two dices didn't work when using -L or -H
  Expressions like "10d10-L" summed some of the values instead of returning the lowest of all values.

• L and H were inverted
  When the results were [1, 2], -L returned 2 and -H returned 1.

[comigor]

Hey @luccasclezar, how are you doing?

This package was based on an old version of JS' rpg-dice-roller package. They used simplified modifiers like -L and -H, which are not common nowadays but could be read as "remove lowest roll" and "remove highest roll" respectively (and could be replaced by nowadays dl1 and dh1, respectively).

If you'd like to properly implement those notations (probably following the up-to-date version of that original package, I can review them and ship on a manjor version of this lib (given there is tests reflecting the new behavior).