[MRG] Fix errors/warnings in tutorial

[ntolley]

@JBHynes @cvargasi as mentioned earlier, this is the mechanism for contributing changes to the existing code. Since my changes are to the .mlx files, you won't be able to inspect them inside github. However, you can git checkout this branch locally to see what's different.

Specifically inside the local folder, you should be able to run:

$ git fetch
$ git checkout development

These commands will first download the "development" branch I have created, and then replace your local files with the changes I have made. If you are ok with what's been changed, you can click the "rebase and merge" button at the bottom of this pull request. This will move the changes from the development branch, to the main ("master") branch.

[ntolley]

Also after merging, you can restore your local files by running git checkout master. Since the master branch will be updated on github, you can run git pull to synchronize the changes with github. At that point the "development" branch is redundant because all the changes are incorporated into the master branch.