Bump cssnano from 7.1.5 to 7.1.7

Bumps [cssnano](https://github.com/cssnano/cssnano) from 7.1.5 to 7.1.7.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@7.1.5...cssnano@7.1.7)

---
updated-dependencies:
- dependency-name: cssnano
  dependency-version: 7.1.7
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -11,7 +11,7 @@
   "devDependencies": {
     "@lodder/grunt-postcss": "3.1.1",
     "autoprefixer": "10.5.0",
-    "cssnano": "7.1.5",
+    "cssnano": "7.1.7",
     "grunt": "1.6.2",
     "grunt-cli": "1.5.0",
     "grunt-concurrent": "3.0.0",