Bug in part 5 blocking movement to occupied tile

[luetkemj]

LOVE the tutorial - super helpful so far. Thanks for putting it together.

I found a bug in step 5. See this PR for a fix. #2

Essentially, monsters are not added with a blocking flag and isUnoccupied is passed incorrect arguments. I think this is fixed in later examples if you just power through but the tutorial suggests you test things before moving on.

Thanks for such a kickass tutorial - hope you finish it 👍