Fixed views_of_a_function validator.

Summary:
views_of_a_function validator expected inexact answers, but didn't
specify the inexact flag, causing it to only succeed on very close
guesses on an irrational function.

Test Plan:
Visit views_of_a_function, make sure that you can complete it for
sin and power functions. Make sure the hint solution works for both
types of function.

Auditors: alex