Tutorial validation: use `-B` when doing a diff between expected/actual output

See https://github.com/confluentinc/kafka-tutorials/pull/579 for more context.

When I build the `window-final-result` tutorial locally, it appears to succeed locally but ultimately fails because the diff isn't exactly -- there are blank lines:

```
cat tutorial-steps/dev/expected-count.txt
5
1
1
2
```

versus

```
cat tutorial-steps/dev/outputs/actual-count.txt
5
1
1
2

```

So this check fails:

```
[16:10:12] ~/git/kafka-tutorials/_includes/tutorials/window-final-result/kstreams/code(GH-461) ✗: bash -c 'diff --strip-trailing-cr <(cat tutorial-steps/dev/expected-count.txt) <(cat tutorial-steps/dev/outputs/actual-count.txt)'

4a5,7
>
>
>
[16:10:20] ~/git/kafka-tutorials/_includes/tutorials/window-final-result/kstreams/code(GH-461) ✗: echo $?
1

```

But this check passes (Notice the addition of the `-B` flag):

```
[16:10:22] ~/git/kafka-tutorials/_includes/tutorials/window-final-result/kstreams/code(GH-461) ✗: bash -c 'diff -B --strip-trailing-cr <(cat tutorial-steps/dev/expected-count.txt) <(cat tutorial-steps/dev/outputs/actual-count.txt)'

[16:10:35] ~/git/kafka-tutorials/_includes/tutorials/window-final-result/kstreams/code(GH-461) ✗: echo $?
0

```