Check score recursively only if both sides are objects

Otherwise, missing sub-objects or arrays can cause an error.

lib/scoreProperties.js

@@ -20,7 +20,7 @@ function scorePrimitiveProperty(expectation, result, weight) {
  * through all the keys, calculating the subscores, and aggregating them
  */
 function scoreProperties(expectation, result, weight) {
-  if (isObject(expectation)) {
+  if (isObject(expectation) && isObject(result)) {
     weight = weight || {};
     var subscores = Object.keys(expectation).map(function(property){
       return scoreProperties(expectation[property], result[property], weight[property]);