ZOOKEEPER-4007: A typo in the ZKUtil#validateFileInput method

Author: fangxiao <benec.fx@gmail.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>,  maoling <maoling@apache.org>

Closes #1687 from benecdict-fang/ZOOKEEPER-4007

zookeeper-server/src/main/java/org/apache/zookeeper/ZKUtil.java

@@ -163,7 +163,7 @@ public class ZKUtil {
             return "Read permission is denied on the file '" + file.getAbsolutePath() + "'";
         }
         if (file.isDirectory()) {
-            return "'" + file.getAbsolutePath() + "' is a direcory. it must be a file.";
+            return "'" + file.getAbsolutePath() + "' is a directory. it must be a file.";
         }
         return null;
     }

zookeeper-server/src/test/java/org/apache/zookeeper/ZKUtilTest.java

@@ -67,7 +67,7 @@ public class ZKUtilTest {
         String absolutePath = file.getAbsolutePath();
         String error = ZKUtil.validateFileInput(absolutePath);
         assertNotNull(error);
-        String expectedMessage = "'" + absolutePath + "' is a direcory. it must be a file.";
+        String expectedMessage = "'" + absolutePath + "' is a directory. it must be a file.";
         assertEquals(expectedMessage, error);
     }