Increase reactant drop rate for excavation missions

[hotbeast]

Some excavation mission have inconsistent spawns and the map is huge. Coupled with the decrease in spawn rate if no drills are active makes it annoying. This isn't that much of a problem in normal missions but in void fissures it makes collecting reactant a pain. Most people spread out in these missions and reactant is spread thin. I've been in a lot of missions where complains are thrown around about how the excavator energy is full before everyone's reactant is filled.