Merge pull request #757 from textpattern/dependabot/npm_and_yarn/cssnano-7.1.7

Bump cssnano from 7.1.5 to 7.1.7

Author: petecooper

package.json

@@ -12,7 +12,7 @@
   "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",