fix(merge): treat dates as atomic values instead of objects.

Makes angular.merge copy dates correctly.

Closes #11720

Author: gabrielmaldi

src/Angular.js

@@ -335,8 +335,12 @@ function baseExtend(dst, objs, deep) {
       var src = obj[key];
 
       if (deep && isObject(src)) {
-        if (!isObject(dst[key])) dst[key] = isArray(src) ? [] : {};
-        baseExtend(dst[key], [src], true);
+        if (isDate(src)) {
+          dst[key] = new Date(src.valueOf());
+        } else {
+          if (!isObject(dst[key])) dst[key] = isArray(src) ? [] : {};
+          baseExtend(dst[key], [src], true);
+        }
       } else {
         dst[key] = src;
       }