Bump httpclient from 4.5.12 to 4.5.13 in /plugins/gradle/example-client (#341)

plugins/gradle/example-client/build.gradle

@@ -24,7 +24,7 @@ dependencies {
     // https://search.maven.org/artifact/io.github.kobylynskyi/graphql-java-codegen
     implementation "io.github.kobylynskyi:graphql-java-codegen:3.1.2-SNAPSHOT"
 
-    implementation "org.apache.httpcomponents:httpclient:4.5.12"
+    implementation "org.apache.httpcomponents:httpclient:4.5.13"
     implementation "javax.validation:validation-api:2.0.1.Final"
 
     implementation "org.mapstruct:mapstruct:1.4.0.Final"