Fix broken expectation in Safari for serializing invalid dates.

src/Angular.js

@@ -1169,6 +1169,8 @@ function toJsonReplacer(key, value) {
     val = '$DOCUMENT';
   } else if (isScope(value)) {
     val = '$SCOPE';
+  } else if (isDate(value) && isNaN(value.getMilliseconds())) {
+    val = null;
   }
 
   return val;

test/AngularSpec.js

@@ -2058,6 +2058,10 @@ describe('angular', function() {
     it('should serialize undefined as undefined', function() {
       expect(toJson(undefined)).toEqual(undefined);
     });
+
+    it('should serialize invalid dates to null', function() {
+      expect(toJson({when: new Date(1 / 0)})).toEqual('{"when":null}');
+    });
   });
 
   describe('isElement', function() {