fix-memoryleak

Author: Oliverwqcwrw

src/main/java/org/apache/ibatis/session/SqlSessionManager.java

@@ -333,7 +333,7 @@ public void close() {
     try {
       sqlSession.close();
     } finally {
-      localSqlSession.set(null);
+      localSqlSession.remove();
     }
   }