Bump elliptic from 6.5.4 to 6.5.7

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.5.4 to 6.5.7.
- [Commits](indutny/elliptic@v6.5.4...v6.5.7)

---
updated-dependencies:
- dependency-name: elliptic
  dependency-type: direct:production
...

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

package.json

@@ -11,7 +11,7 @@
     "acorn": "^6.4.1",
     "browserify": "^14.5.0",
     "cached-path-relative": ">=1.1.0",
-    "elliptic": ">=6.5.4",
+    "elliptic": ">=6.5.7",
     "minimist": "^1.2.8",
     "qrious": "^4.0.2",
     "ripple-keypairs": "^1.3.1"