feat: Use ursa-optional as dependency

package.json

@@ -39,13 +39,10 @@
   },
   "homepage": "https://git.coolaj86.com/coolaj86/rsa-compat.js#readme",
   "dependencies": {
-    "node-forge": "^0.6.41"
-  },
-  "optionalDependencies": {
+    "node-forge": "^0.6.41",
+    "ursa-optional": "^0.9.6"
   },
   "trulyOptionalDependencies": {
-    "buffer-v6-polyfill": "^1.0.3",
-    "ursa": "^0.9.4",
-    "ursa-optional": "^0.9.4"
+    "buffer-v6-polyfill": "^1.0.3"
   }
 }