Bump graphql-java-extended-scalars in /plugins/gradle/example-server (#371)

Bumps [graphql-java-extended-scalars](https://github.com/graphql-java/graphql-java-extended-scalars) from 1.1.0 to 15.0.0.
- [Release notes](https://github.com/graphql-java/graphql-java-extended-scalars/releases)
- [Commits](https://github.com/graphql-java/graphql-java-extended-scalars/compare/1.1.0...15.0.0)
Signed-off-by: Ndependabot[bot] <support@github.com>
Co-authored-by: Ndependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

plugins/gradle/example-server/build.gradle

@@ -17,7 +17,7 @@ dependencies {
 
     implementation "com.graphql-java-kickstart:graphql-spring-boot-starter:8.0.0"
     implementation "com.graphql-java-kickstart:graphiql-spring-boot-starter:8.0.0"
-    implementation "com.graphql-java:graphql-java-extended-scalars:1.1.0"
+    implementation "com.graphql-java:graphql-java-extended-scalars:15.0.0"
 
     implementation "javax.validation:validation-api:2.0.1.Final"