[skip ci] specify source/target in example pom.xml (#2762)

Signed-off-by: Henry Avetisyan <[email protected]>

clients/java/zts/examples/tls-support/pom.xml

@@ -78,6 +78,15 @@
 
   <build>
     <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.13.0</version>
+        <configuration>
+          <source>11</source>
+          <target>11</target>
+        </configuration>
+      </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-dependency-plugin</artifactId>