Bump xstream from 1.4.7 to 1.4.15 in /library-service-rest-frontend#8

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dependabot/maven/library-service-rest-frontend/com.thoughtworks.xstream-xstream-1.4.15ApolloDev/apollo-library-services:dependabot/maven/library-service-rest-frontend/com.thoughtworks.xstream-xstream-1.4.15Copy head branch name to clipboard