Fix coach report answer correctness color

Summary:
Addresses issue (https://code.google.com/p/khanacademy/issues/detail?id=23292) / task (http://phabricator.khanacademy.org/T1877)

Maybe at some point the validator just returned true/false; now it returns an object, of which x.correct returns true/false.

Possible Concerns:
Do I need to check that the object exists? I don't think so, because if there is a validator to begin with, it should return an object (as far as I know in Perseus)

I'd push, but I forgot my Github password and was too lazy to reset it.

Test Plan: (1) Check that it's the right color

Reviewers: alex

Reviewed By: alex

Subscribers: alpert, khirasaki

Differential Revision: http://phabricator.khanacademy.org/D7616

history.js

@@ -161,7 +161,7 @@ function renderReadOnlyProblem(event, args) {
                                   (guess.value != null ? guess.value : guess) +
                                   "</p>").runModules()
                             );
-                            if (validator(guess)) {
+                            if (validator(guess).correct) {
                                 thissolutionarea
                                     .removeClass("incorrect-activity")
                                     .addClass("correct-activity");
@@ -170,7 +170,7 @@ function renderReadOnlyProblem(event, args) {
                                 thissolutionarea.attr("title", $._("Incorrect Answer"));
                             }
                         } else if (answerType === "custom") {
-                            if (validator(guess)) {
+                            if (validator(guess).correct) {
                                 thissolutionarea
                                     .removeClass("incorrect-activity")
                                     .addClass("correct-activity");
@@ -192,7 +192,7 @@ function renderReadOnlyProblem(event, args) {
 
                             thisAnswerData.showGuess(guess);
 
-                            if (thisAnswerData.validator(guess) === true) {
+                            if (thisAnswerData.validator(guess).correct) {
                                 // If the user didn't get the problem right on the first try, all
                                 // answers are labelled incorrect by default
                                 thissolutionarea