[Kotlin Server] Fix Ktor and modelMutable samples #5

Job	Run time
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot)	1m 26s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-multipart-request-model)	1m 36s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-bigdecimal-default)	1m 22s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-delegate)	1m 26s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-modelMutable)	1m 28s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-reactive)	1m 31s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-source-swagger1)	1m 33s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-source-swagger2)	1m 38s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-springboot-springfox)	1m 39s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-server/ktor)	1m 34s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-server/jaxrs-spec)	1m 5s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-server/jaxrs-spec-mutiny)	56s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-server-modelMutable)	1m 25s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-server/javalin)	1m 18s
Build Kotlin server (jdk8) (samples/server/others/kotlin-server/jaxrs-spec)	1m 7s
Build Kotlin server (jdk8) (samples/server/others/kotlin-server/jaxrs-spec-array-response)	1m 10s
Build Kotlin server (jdk8) (samples/server/petstore/kotlin-spring-cloud)	1m 27s
	23m 41s

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