Bump grunt from 1.0.4 to 1.5.3

Bumps [grunt](https://github.com/gruntjs/grunt) from 1.0.4 to 1.5.3.
- [Release notes](https://github.com/gruntjs/grunt/releases)
- [Changelog](https://github.com/gruntjs/grunt/blob/main/CHANGELOG)
- [Commits](https://github.com/gruntjs/grunt/compare/v1.0.4...v1.5.3)

---
updated-dependencies:
- dependency-name: grunt
  dependency-type: direct:development
...

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

package.json

@@ -15,7 +15,7 @@
     "url": "https://github.com/mozilla/fxa-content-server-l10n/issues"
   },
   "devDependencies": {
-    "grunt": "^1.0.4",
+    "grunt": "^1.5.3",
     "grunt-l10n-lint": "0.0.3",
     "load-grunt-tasks": "^5.1.0",
     "time-grunt": "^2.0.0"