NumericInput: Fix grading

Summary:
While adding acceptable formats to numeric-input, I forgot to change
the parameter name to a function, which caused a javascript error on
changing the numeric input's value, and made numeric-inputs always
grade as empty.

This commit fixes this parameter name to get rid of the javascript
error and fix numeric-input grading

Test Plan:
 * See [item](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22On%20a%20beautiful%20afternoon%2C%20Ashley%20rode%20her%20bicycle%20to%20a%20farm%20that%20sold%20baskets%20of%20apples%20for%20%24%5C%5C%246.89%24%20each%20and%20baskets%20of%20bananas%20for%20%24%5C%5C%244.78%24%20each.%5Cn%5CnAshley%20decided%20to%20buy%20a%20basket%20of%20apples%20and%20a%20basket%20of%20bananas%20.%5Cn%5Cn**How%20much%20did%20Ashley%20need%20to%20pay%20for%20her%20produce%3F**%5Cn%5Cn%24%5C%5C%24%24%20%5B%5B%E2%98%83%20numeric-input%201%5D%5D%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22numeric-input%201%22%3A%7B%22type%22%3A%22numeric-input%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22answers%22%3A%5B%7B%22value%22%3A11.67%2C%22status%22%3A%22correct%22%2C%22message%22%3A%22great%20job%22%2C%22simplify%22%3A%22required%22%2C%22strict%22%3Afalse%2C%22maxError%22%3Anull%7D%2C%7B%22value%22%3A2.11%2C%22status%22%3A%22wrong%22%2C%22message%22%3A%22It%20looks%20like%20you%20subtracted.%20Ashley%20bought%20two%20baskets%20of%20fruit%2C%20so%20we%20add%20the%20prices%20of%20each%20to%20find%20the%20total%20cost.%22%2C%22simplify%22%3A%22required%22%2C%22strict%22%3Afalse%2C%22maxError%22%3Anull%7D%5D%2C%22size%22%3A%22normal%22%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22Fill%20in%20the%20blank.%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22hints%22%3A%5B%5D%7D)
 * try grading "5", "11.67", and "2.11"

Auditors: alex