HADOOP-14355. Update maven-war-plugin to 3.1.0.

hadoop-project/pom.xml

@@ -126,7 +126,7 @@
     <maven-resources-plugin.version>2.6</maven-resources-plugin.version>
     <maven-shade-plugin.version>2.4.3</maven-shade-plugin.version>
     <maven-jar-plugin.version>2.5</maven-jar-plugin.version>
-    <maven-war-plugin.version>2.4</maven-war-plugin.version>
+    <maven-war-plugin.version>3.1.0</maven-war-plugin.version>
     <maven-source-plugin.version>2.3</maven-source-plugin.version>
     <maven-pdf-plugin.version>1.2</maven-pdf-plugin.version>
     <maven-remote-resources-plugin.version>1.5</maven-remote-resources-plugin.version>