Fix ./pants to ./pants goal gaols in tutorial.

Fix ./pants to ./pants goal goals

Since ./pants gives you an error saying no goals to prepare.

Reviewed at https://rbcommons.com/s/twitter/r/1427/
Sync of https://github.com/pantsbuild/pants/commit/0cf79b62796b7b509e93c01ea61b66b11a55dc0d