Bump io.undertow:undertow-core in /samples/server/petstore/java-undertow #216

Job	Run time
Build Java Server (samples/server/petstore/java-vertx-web/)	1m 3s
Build Java Server (samples/server/petstore/java-microprofile/)	1m 29s
Build Java Server (samples/server/petstore/java-inflector/)	1m 13s
Build Java Server (samples/server/petstore/java-pkmst/)	1m 25s
	5m 10s

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