Val'kyr Twins Bug Fixes

The following bug fixes to Val'kyr Twins were just deployed, and they will increase the overall difficulty of the encounter.

- Surge of Light and Surge of Darkness were not being cast properly on Normal difficulties.
- Light Vortex was doing less damage than Dark Vortex.

Along with those two major bug fixes, we also increased the rate with which the Concentrated Light and Concentrated Darkness spawns.