fix(build) exit with error if any CSS step fails
fix(build) exit with error if any CSS step fails

Before:

~~~
$ make deploy-css
./node_modules/.bin/sass css/main.scss css/all.bundle.css && \
        ./node_modules/.bin/cleancss --skip-rebase css/all.bundle.css > css/all.css ; \
        rm css/all.bundle.css
Error: Can't find stylesheet to import.
   ╷
78 │ @import 'filmstrip/vertical_filmstrip_overrides2';
   │         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  css/main.scss 78:9  root stylesheet
$
(exitcode is 0)
~~~

After:

~~~
$ make deploy-css
./node_modules/.bin/sass css/main.scss css/all.bundle.css && \
        ./node_modules/.bin/cleancss --skip-rebase css/all.bundle.css > css/all.css && \
        rm css/all.bundle.css
Error: Can't find stylesheet to import.
   ╷
78 │ @import 'filmstrip/vertical_filmstrip_overrides2';
   │         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  css/main.scss 78:9  root stylesheet
make: *** [deploy-css] Error 65
$
(exitcode is != 0)
~~~

jitsi/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet