test: Fix active user test for InmemoryDB (#603)

Author: KShivendu

src/test/java/io/supertokens/test/ActiveUsersTest.java

@@ -55,6 +55,8 @@ public void updateAndCountUserLastActiveTest() throws Exception {
 
         assert ActiveUsers.countUsersActiveSince(main, now) == 2;
 
+        Thread.sleep(100);
+
         long now2 = System.currentTimeMillis();
 
         ActiveUsers.updateLastActive(main, "user1");