Don't go to 10; it's too hard to see

Summary:
It's hard to see the blue dot at http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/complex_number_polar_form_intuition.html?seed=88&problem=0.

Fixes #55664.

Reviewers: eater

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D3229