slide tweaks based on class feedback.

test probably lives in tests. newline. TDesai points out: 'foo' is not a great example. A slide for showing addresses in a BUILD file.

Testing Done:
viewed slides on laptop in not-so-many-pixels mode. slides fit onscreen, yay

Reviewed at https://rbcommons.com/s/twitter/r/1532/
Sync of https://github.com/pantsbuild/pants/commit/02490803b281a88e0b50b86e846e935a0b680867