Bump elliptic from 6.4.1 to 6.5.3 in /libs/stellar-util

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.4.1 to 6.5.3.
- [Release notes](https://github.com/indutny/elliptic/releases)
- [Commits](https://github.com/indutny/elliptic/compare/v6.4.1...v6.5.3)

Signed-off-by: dependabot[bot] <support@github.com>

libs/stellar-util/package-lock.json

@@ -581,9 +581,9 @@
       }
     },
     "elliptic": {
-      "version": "6.4.1",
-      "resolved": "https://registry.npmjs.org/elliptic/-/elliptic-6.4.1.tgz",
-      "integrity": "sha512-BsXLz5sqX8OHcsh7CqBMztyXARmGQ3LWPtGjJi6DiJHq5C/qvi9P3OqgswKSDftbu8+IoI/QDTAm2fFnQ9SZSQ==",
+      "version": "6.5.3",
+      "resolved": "https://registry.npmjs.org/elliptic/-/elliptic-6.5.3.tgz",
+      "integrity": "sha512-IMqzv5wNQf+E6aHeIqATs0tOLeOTwj1QKbRcS3jBbYkl5oLAserA8yJTT7/VyHUYG91PRmPyeQDObKLPpeS4dw==",
       "dev": true,
       "requires": {
         "bn.js": "^4.4.0",