Bump elliptic from 6.5.4 to 6.5.7 in /themes/custom/apigee_kickstart (apigee#699)

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: indirect
...

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