switch plugin specification and position, according to Shine recommendation

package.json

@@ -23,9 +23,9 @@
   "license": "(OFL-1.1 AND MIT)",
   "dependencies": {},
   "devDependencies": {
-    "less-plugin-clean-css": "^1.5.1",
     "all-contributors-cli": "^6.16.0",
     "less": "^3.11.3",
+    "less-plugin-clean-css": "less/less-plugin-clean-css#master",
     "svgo": "^1.3.2"
   },
   "engines": {