Bump graphiql-spring-boot-starter in /plugins/gradle/example-server (#213)

Bumps [graphiql-spring-boot-starter](https://github.com/graphql-java-kickstart/graphql-spring-boot) from 7.0.1 to 7.1.0.
- [Release notes](https://github.com/graphql-java-kickstart/graphql-spring-boot/releases)
- [Commits](https://github.com/graphql-java-kickstart/graphql-spring-boot/compare/v7.0.1...v7.1.0)
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Co-authored-by: Ndependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

plugins/gradle/example-server/build.gradle

@@ -16,7 +16,7 @@ dependencies {
     implementation "org.springframework.boot:spring-boot-starter-data-mongodb:2.3.1.RELEASE"
 
     implementation "com.graphql-java-kickstart:graphql-spring-boot-starter:7.1.0"
-    implementation "com.graphql-java-kickstart:graphiql-spring-boot-starter:7.0.1"
+    implementation "com.graphql-java-kickstart:graphiql-spring-boot-starter:7.1.0"
 
     implementation "javax.validation:validation-api:2.0.1.Final"