build(deps): bump postcss from 7.0.27 to 7.0.28

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.27 to 7.0.28.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/master/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.27...7.0.28)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

yarn.lock

@@ -5805,9 +5805,9 @@ postcss@^6.0.1:
     supports-color "^5.4.0"
 
 postcss@^7.0.1, postcss@^7.0.27:
-  version "7.0.27"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.27.tgz#cc67cdc6b0daa375105b7c424a85567345fc54d9"
-  integrity sha512-WuQETPMcW9Uf1/22HWUWP9lgsIC+KEHg2kozMflKjbeUtw9ujvFX6QmIfozaErDkmLWS9WEnEdEe6Uo9/BNTdQ==
+  version "7.0.28"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.28.tgz#d349ced7743475717ba91f6810efb58c51fb5dbb"
+  integrity sha512-YU6nVhyWIsVtlNlnAj1fHTsUKW5qxm3KEgzq2Jj6KTEFOTK8QWR12eIDvrlWhiSTK8WIBFTBhOJV4DY6dUuEbw==
   dependencies:
     chalk "^2.4.2"
     source-map "^0.6.1"