caches: Don't depend on yarn.lock existing.
caches: Don't depend on yarn.lock existing.

This allows our cache cleaning code to run on servers that have copies
of Zulip 1.6 and older around.

brockwhittaker/zulip,synicalsyntax/zulip,eeshangarg/zulip,shubhamdhama/zulip,Galexrt/zulip,kou/zulip,amanharitsh123/zulip,synicalsyntax/zulip,showell/zulip,timabbott/zulip,brockwhittaker/zulip,eeshangarg/zulip,kou/zulip,hackerkid/zulip,brainwane/zulip,Galexrt/zulip,zulip/zulip,rht/zulip,timabbott/zulip,hackerkid/zulip,andersk/zulip,jackrzhang/zulip,andersk/zulip,dhcrzf/zulip,hackerkid/zulip,dhcrzf/zulip,mahim97/zulip,rishig/zulip,brockwhittaker/zulip,brainwane/zulip,eeshangarg/zulip,rht/zulip,tommyip/zulip,timabbott/zulip,verma-varsha/zulip,punchagan/zulip,amanharitsh123/zulip,timabbott/zulip,synicalsyntax/zulip,andersk/zulip,rishig/zulip,eeshangarg/zulip,showell/zulip,synicalsyntax/zulip,showell/zulip,punchagan/zulip,verma-varsha/zulip,showell/zulip,dhcrzf/zulip,punchagan/zulip,Galexrt/zulip,rht/zulip,shubhamdhama/zulip,zulip/zulip,shubhamdhama/zulip,brainwane/zulip,hackerkid/zulip,amanharitsh123/zulip,kou/zulip,shubhamdhama/zulip,jackrzhang/zulip,dhcrzf/zulip,verma-varsha/zulip,synicalsyntax/zulip,Galexrt/zulip,showell/zulip,zulip/zulip,synicalsyntax/zulip,rht/zulip,punchagan/zulip,brockwhittaker/zulip,kou/zulip,amanharitsh123/zulip,tommyip/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,verma-varsha/zulip,jackrzhang/zulip,mahim97/zulip,timabbott/zulip,kou/zulip,zulip/zulip,timabbott/zulip,brockwhittaker/zulip,zulip/zulip,andersk/zulip,jackrzhang/zulip,hackerkid/zulip,andersk/zulip,tommyip/zulip,punchagan/zulip,Galexrt/zulip,showell/zulip,brainwane/zulip,shubhamdhama/zulip,zulip/zulip,jackrzhang/zulip,rishig/zulip,dhcrzf/zulip,brainwane/zulip,rishig/zulip,shubhamdhama/zulip,rht/zulip,timabbott/zulip,kou/zulip,eeshangarg/zulip,brainwane/zulip,brockwhittaker/zulip,amanharitsh123/zulip,brainwane/zulip,tommyip/zulip,verma-varsha/zulip,shubhamdhama/zulip,rishig/zulip,andersk/zulip,hackerkid/zulip,hackerkid/zulip,tommyip/zulip,rht/zulip,verma-varsha/zulip,mahim97/zulip,Galexrt/zulip,mahim97/zulip,eeshangarg/zulip,jackrzhang/zulip,kou/zulip,mahim97/zulip,dhcrzf/zulip,showell/zulip,synicalsyntax/zulip,dhcrzf/zulip,tommyip/zulip,mahim97/zulip,punchagan/zulip,rishig/zulip,tommyip/zulip,amanharitsh123/zulip,jackrzhang/zulip,andersk/zulip,rishig/zulip,zulip/zulip,Galexrt/zulip