build-docs: Fix shellcheck warnings.
build-docs: Fix shellcheck warnings.

In tools/build-docs line 3:
cd "$(dirname "$0")"/../docs
^-- SC2164: Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

Signed-off-by: Anders Kaseorg <087231934ba8fcf78bc142ce37d193b895ac03c4@mit.edu>

synicalsyntax/zulip,shubhamdhama/zulip,shubhamdhama/zulip,brainwane/zulip,dhcrzf/zulip,dhcrzf/zulip,hackerkid/zulip,showell/zulip,rht/zulip,punchagan/zulip,rht/zulip,timabbott/zulip,showell/zulip,synicalsyntax/zulip,showell/zulip,shubhamdhama/zulip,jackrzhang/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,hackerkid/zulip,synicalsyntax/zulip,showell/zulip,showell/zulip,jackrzhang/zulip,shubhamdhama/zulip,tommyip/zulip,brainwane/zulip,eeshangarg/zulip,rishig/zulip,hackerkid/zulip,synicalsyntax/zulip,hackerkid/zulip,rht/zulip,andersk/zulip,rishig/zulip,synicalsyntax/zulip,eeshangarg/zulip,zulip/zulip,punchagan/zulip,timabbott/zulip,jackrzhang/zulip,rht/zulip,hackerkid/zulip,rishig/zulip,jackrzhang/zulip,kou/zulip,andersk/zulip,andersk/zulip,tommyip/zulip,kou/zulip,showell/zulip,tommyip/zulip,zulip/zulip,brainwane/zulip,rht/zulip,showell/zulip,punchagan/zulip,rishig/zulip,eeshangarg/zulip,eeshangarg/zulip,jackrzhang/zulip,rishig/zulip,rishig/zulip,timabbott/zulip,synicalsyntax/zulip,brainwane/zulip,timabbott/zulip,rishig/zulip,zulip/zulip,jackrzhang/zulip,shubhamdhama/zulip,andersk/zulip,zulip/zulip,dhcrzf/zulip,rht/zulip,punchagan/zulip,andersk/zulip,kou/zulip,andersk/zulip,rht/zulip,tommyip/zulip,punchagan/zulip,timabbott/zulip,brainwane/zulip,tommyip/zulip,brainwane/zulip,andersk/zulip,punchagan/zulip,tommyip/zulip,synicalsyntax/zulip,jackrzhang/zulip,tommyip/zulip,hackerkid/zulip,eeshangarg/zulip,dhcrzf/zulip,brainwane/zulip,dhcrzf/zulip,dhcrzf/zulip,shubhamdhama/zulip,kou/zulip,timabbott/zulip,punchagan/zulip,shubhamdhama/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,timabbott/zulip,kou/zulip,dhcrzf/zulip,kou/zulip