Bump grunt from 1.5.3 to 1.6.1

Bumps [grunt](https://github.com/gruntjs/grunt) from 1.5.3 to 1.6.1.
- [Release notes](https://github.com/gruntjs/grunt/releases)
- [Changelog](https://github.com/gruntjs/grunt/blob/main/CHANGELOG)
- [Commits](gruntjs/grunt@v1.5.3...v1.6.1)

---
updated-dependencies:
- dependency-name: grunt
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

package.json

@@ -10,7 +10,7 @@
     "url": "https://github.com/textpattern/textpattern-plugins-website/issues"
   },
   "devDependencies": {
-    "grunt": "1.5.3",
+    "grunt": "1.6.1",
     "grunt-cli": "1.4.3",
     "grunt-concurrent": "3.0.0",
     "grunt-contrib-clean": "2.0.1",