timerender: Make moment() return static date.
timerender: Make moment() return static date.

The previous iteration of the test was flaky when we could get
off by one errors between two moment() calls.

kou/zulip,hackerkid/zulip,showell/zulip,brainwane/zulip,eeshangarg/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,rht/zulip,showell/zulip,kou/zulip,kou/zulip,kou/zulip,punchagan/zulip,showell/zulip,showell/zulip,andersk/zulip,zulip/zulip,zulip/zulip,kou/zulip,andersk/zulip,kou/zulip,punchagan/zulip,eeshangarg/zulip,brainwane/zulip,showell/zulip,rht/zulip,brainwane/zulip,zulip/zulip,punchagan/zulip,punchagan/zulip,eeshangarg/zulip,eeshangarg/zulip,showell/zulip,punchagan/zulip,brainwane/zulip,punchagan/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,andersk/zulip,zulip/zulip,brainwane/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,showell/zulip,eeshangarg/zulip,hackerkid/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,brainwane/zulip,andersk/zulip,rht/zulip,rht/zulip,hackerkid/zulip,andersk/zulip,rht/zulip