Fix issue building UI for production env
Fix issue building UI for production env

Building the UI for production (via the `yarn build` script) involves
using [cssnano][0] to compress the UI stylesheets. Previously, cssnano
errored on some [invalid SCSS syntax][1], causing the entire production
build to fail. This also broke the `deploy` workflow in CircleCI.

This commit fixes the invalid SCSS syntax and resulting issues.

Closes #1553

[0]: https://cssnano.co/
[1]: https://github.com/sass/sass/issues/818

li-ang/influxdb,nooproblem/influxdb,nooproblem/influxdb,influxdb/influxdb,influxdb/influxdb,nooproblem/influxdb,nooproblem/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,influxdata/influxdb,mark-rushakoff/influxdb,nooproblem/influxdb,influxdb/influxdb,influxdb/influxdb,li-ang/influxdb,mark-rushakoff/influxdb,influxdata/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb