Update package.json

bump `grunt` to address 2x Dependabot issues

Author: petecooper

package.json

@@ -14,7 +14,7 @@
     "@squoosh/cli": "0.7.2",
     "autoprefixer": "10.4.2",
     "cssnano": "5.1.1",
-    "grunt": "1.4.1",
+    "grunt": "1.5.3",
     "grunt-cli": "1.4.3",
     "grunt-concurrent": "3.0.0",
     "grunt-contrib-clean": "2.0.0",