Update stale issue comment to mention 6-1-stable
Update stale issue comment to mention 6-1-stable

6-1-stable is the release series that currently receives bug fixes.

kmcphillips/rails,tjschuck/rails,yawboakye/rails,kddeisz/rails,Edouard-chin/rails,bogdanvlviv/rails,yahonda/rails,esparta/rails,betesh/rails,EmmaB/rails-1,MSP-Greg/rails,rails/rails,yawboakye/rails,esparta/rails,Vasfed/rails,tjschuck/rails,Stellenticket/rails,tgxworld/rails,EmmaB/rails-1,tgxworld/rails,esparta/rails,Stellenticket/rails,joonyou/rails,Erol/rails,betesh/rails,Vasfed/rails,tgxworld/rails,kmcphillips/rails,betesh/rails,Edouard-chin/rails,lcreid/rails,Envek/rails,Stellenticket/rails,bogdanvlviv/rails,tjschuck/rails,kmcphillips/rails,kddeisz/rails,MSP-Greg/rails,Erol/rails,BlakeWilliams/rails,rails/rails,kmcphillips/rails,betesh/rails,Envek/rails,esparta/rails,georgeclaghorn/rails,lcreid/rails,rails/rails,yawboakye/rails,EmmaB/rails-1,georgeclaghorn/rails,yahonda/rails,MSP-Greg/rails,Envek/rails,tgxworld/rails,georgeclaghorn/rails,yawboakye/rails,Stellenticket/rails,Erol/rails,Erol/rails,Vasfed/rails,joonyou/rails,BlakeWilliams/rails,rails/rails,lcreid/rails,Vasfed/rails,BlakeWilliams/rails,Edouard-chin/rails,bogdanvlviv/rails,joonyou/rails,kddeisz/rails,lcreid/rails,MSP-Greg/rails,yahonda/rails,georgeclaghorn/rails,yahonda/rails,bogdanvlviv/rails,kddeisz/rails,joonyou/rails,tjschuck/rails,Envek/rails,BlakeWilliams/rails,Edouard-chin/rails