optimize-svg: Fix shellcheck warnings.
optimize-svg: Fix shellcheck warnings.

In tools/optimize-svg line 3:
if [ `node_modules/.bin/svgo -f static/images/integrations/logos | grep -o '\.[0-9]% = ' | wc -l` -ge 1 ]
     ^-- SC2046: Quote this to prevent word splitting.
     ^-- SC2006: Use $(..) instead of legacy `..`.

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

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