change the type of ask_who parameter in TriggerSkill::triggerable()

from ServerPlayer * 2 ServerPlayer * &
Merge branch 'master' of https://github.com/Fsu0413/QSanguosha-For-Hegemony

Conflicts:
	src/package/standard-wei-generals.cpp
	src/package/standard-wu-generals.cpp
	src/package/wind.cpp