Bumpup war plugin version. (#2878)

java/demo/pom.xml

@@ -101,6 +101,11 @@
         </configuration>
         <groupId>org.apache.maven.plugins</groupId>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-war-plugin</artifactId>
+        <version>3.3.1</version>
+      </plugin>
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>exec-maven-plugin</artifactId>