Fix validation for views of a function

Here is a fix for the Views of Function bug.

Turned out I set the `maxError` wrong and it was using the default, which was too precise for some of the `graph-to-table` problems. I should have caught this issue early on, but I overlooked the `graph-to-table` problem type.

Here are the `graph-to-table` problems I tested on:

- http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/views_of_a_function.html?debug&problem=graph-to-table&seed=165

- http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/views_of_a_function.html?debug&problem=graph-to-table&seed=43

I also tested the other two problem types.