Fix #12: pin uglify-js

Author: JanStrauss

package.json

@@ -14,6 +14,6 @@
     "devDependencies": {
         "tsc-watch": "^4.2.9",
         "typescript": "^4.1.3",
-        "uglify-js": "^3.12.5"
+        "uglify-js": "3.12.5"
     }
 }