Bump postcss from 8.2.14 to 8.2.15 (#63)

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.14 to 8.2.15.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.2.14...8.2.15)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -19,7 +19,7 @@
     "gulp-svgmin": "^3.0.0",
     "gulp-uglify": "^3.0.0",
     "plugin-error": "^1.0.1",
-    "postcss": "^8.2.14",
+    "postcss": "^8.2.15",
     "request": "^2.79.0",
     "request-promise-native": "^1.0.3"
   },