Add template argument default value for RedisStringCollection.
Add template argument default value for RedisStringCollection.

rejectedsoftware/vibe.d,AndreyMZ/vibe.d,DBankov/vibe.d,chalucha/vibe.d,etcimon/vibe.d,gedaiu/vibe.d,Geod24/vibe.d,etcimon/vibe.d