[modify] update rails to 5.2.6 to fix vulnerability (#3970)
[modify] update rails to 5.2.6 to fix vulnerability (#3970)

also updates dependencies
shirasagi/shirasagi,shirasagi/shirasagi,tany/ss,sunny4381/shirasagi,ShinjiTanimoto/shirasagi,shirasagi/shirasagi,sunny4381/shirasagi,ShinjiTanimoto/shirasagi,tany/ss,ShinjiTanimoto/shirasagi,shirasagi/shirasagi,ShinjiTanimoto/shirasagi,sunny4381/shirasagi,tany/ss,tany/ss,sunny4381/shirasagi