Bumps [spring-core](https://github.com/spring-projects/spring-framework) from 4.1.2.RELEASE to 4.3.21.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v4.1.2.RELEASE...v4.3.21.RELEASE)

---
updated-dependencies:
- dependency-name: org.springframework:spring-core
  dependency-type: direct:production
...

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