fix(ngClass): fix shallowCopy of mixed array and object

Author: drpicox

src/ng/directive/ngClass.js

@@ -78,7 +78,11 @@ function classDirective(name, selector) {
               updateClasses(oldClasses, newClasses);
             }
           }
-          oldVal = shallowCopy(newVal);
+          if (isArray(newVal)) {
+            oldVal = newVal.map(function(v) { return shallowCopy(v); });
+          } else {
+            oldVal = shallowCopy(newVal);
+          }
         }
       }
     };