mypy: Add comment for future use of Deque.
mypy: Add comment for future use of Deque.

In the future, the type annotation should use Deque in order to be
compatible with the latest mypy version. See
https://github.com/python/mypy/pull/2845 for more info.

shubhamdhama/zulip,eeshangarg/zulip,synicalsyntax/zulip,jrowan/zulip,rht/zulip,showell/zulip,andersk/zulip,amanharitsh123/zulip,verma-varsha/zulip,synicalsyntax/zulip,andersk/zulip,zulip/zulip,vaidap/zulip,zulip/zulip,shubhamdhama/zulip,vaidap/zulip,kou/zulip,christi3k/zulip,verma-varsha/zulip,vaidap/zulip,vabs22/zulip,mahim97/zulip,hackerkid/zulip,christi3k/zulip,rht/zulip,vabs22/zulip,hackerkid/zulip,eeshangarg/zulip,j831/zulip,zulip/zulip,andersk/zulip,jrowan/zulip,dhcrzf/zulip,zulip/zulip,punchagan/zulip,christi3k/zulip,kou/zulip,verma-varsha/zulip,shubhamdhama/zulip,vaidap/zulip,rishig/zulip,zulip/zulip,amanharitsh123/zulip,tommyip/zulip,showell/zulip,brainwane/zulip,eeshangarg/zulip,jrowan/zulip,brainwane/zulip,eeshangarg/zulip,synicalsyntax/zulip,dhcrzf/zulip,synicalsyntax/zulip,dhcrzf/zulip,punchagan/zulip,brainwane/zulip,rishig/zulip,timabbott/zulip,rishig/zulip,j831/zulip,zulip/zulip,kou/zulip,Galexrt/zulip,timabbott/zulip,rishig/zulip,verma-varsha/zulip,zulip/zulip,mahim97/zulip,showell/zulip,jrowan/zulip,tommyip/zulip,rht/zulip,eeshangarg/zulip,brainwane/zulip,jackrzhang/zulip,dhcrzf/zulip,rht/zulip,mahim97/zulip,j831/zulip,jrowan/zulip,jackrzhang/zulip,Galexrt/zulip,dhcrzf/zulip,christi3k/zulip,j831/zulip,rishig/zulip,mahim97/zulip,brainwane/zulip,jrowan/zulip,brockwhittaker/zulip,rishig/zulip,rht/zulip,jackrzhang/zulip,dhcrzf/zulip,andersk/zulip,verma-varsha/zulip,rht/zulip,vabs22/zulip,punchagan/zulip,vabs22/zulip,showell/zulip,eeshangarg/zulip,tommyip/zulip,tommyip/zulip,brainwane/zulip,amanharitsh123/zulip,timabbott/zulip,showell/zulip,shubhamdhama/zulip,verma-varsha/zulip,vaidap/zulip,andersk/zulip,j831/zulip,christi3k/zulip,rht/zulip,hackerkid/zulip,tommyip/zulip,punchagan/zulip,andersk/zulip,Galexrt/zulip,brockwhittaker/zulip,brockwhittaker/zulip,hackerkid/zulip,synicalsyntax/zulip,j831/zulip,showell/zulip,synicalsyntax/zulip,mahim97/zulip,jackrzhang/zulip,amanharitsh123/zulip,hackerkid/zulip,christi3k/zulip,andersk/zulip,timabbott/zulip,Galexrt/zulip,amanharitsh123/zulip,shubhamdhama/zulip,kou/zulip,kou/zulip,dhcrzf/zulip,jackrzhang/zulip,kou/zulip,hackerkid/zulip,Galexrt/zulip,tommyip/zulip,punchagan/zulip,brockwhittaker/zulip,rishig/zulip,timabbott/zulip,tommyip/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,jackrzhang/zulip,shubhamdhama/zulip,mahim97/zulip,timabbott/zulip,shubhamdhama/zulip,vabs22/zulip,amanharitsh123/zulip,Galexrt/zulip,vaidap/zulip,brockwhittaker/zulip,hackerkid/zulip,vabs22/zulip,eeshangarg/zulip,brainwane/zulip,brockwhittaker/zulip,jackrzhang/zulip,punchagan/zulip,Galexrt/zulip,kou/zulip,synicalsyntax/zulip