Update jackson-core to version 2.15.0 for security reasons

[mardukbp]

Version 2.8.7 has 2 vulnerabilities and therefore cannot be installed in an enterprise environment. This prevents using transit-java, transit-clj and libraries depending on it, like shadow-cljs, in an enterprise environment with high security standards.

Version 2.15.0 is the oldest version with no known vulnerabilities as of today.