HADOOP-14156. Fix grammar error in ConfTest.java.

This closes #187

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ConfTest.java

@@ -269,7 +269,7 @@ public final class ConfTest {
     } else {
       String confDirName = System.getenv(HADOOP_CONF_DIR);
       if (confDirName == null) {
-        terminate(1, HADOOP_CONF_DIR + " does not defined");
+        terminate(1, HADOOP_CONF_DIR + " is not defined");
       }
       File confDir = new File(confDirName);
       if (!confDir.isDirectory()) {