docs: fix 'occured' -> 'occurred' in LocallyCachedBlob Javadoc

Single-word spelling correction on the cleanup() method Javadoc.

No functional changes.

Signed-off-by: Sai Asish Y <say.apm35@gmail.com>

Author: SAY-5

storm-server/src/main/java/org/apache/storm/localizer/LocallyCachedBlob.java

@@ -159,7 +159,7 @@ protected DownloadMeta fetch(ClientBlobStore store, String key,
     protected abstract void commitNewVersion(long version) throws IOException;
 
     /**
-     * Clean up any temporary files.  This will be called after updating a blob, either successfully or if an error has occured.
+     * Clean up any temporary files.  This will be called after updating a blob, either successfully or if an error has occurred.
      * The goal is to find any files that may be left over and remove them so space is not leaked.
      * PRECONDITION: this can only be called with a lock on this instance held.
      */