specificy less-plugin-clean-css dependency

package.json

@@ -26,6 +26,7 @@
     "@wikimedia/less-plugin-clean-css": "^1.5.2",
     "all-contributors-cli": "^6.16.0",
     "less": "^3.11.3",
+    "less-plugin-clean-css": "^1.5.1",
     "svgo": "^1.3.2"
   },
   "engines": {