fix(plugins): have counter-cache use correct way of defining default values

lib/plugins/counter-cache.js

@@ -45,16 +45,13 @@ module.exports = (function() {
 
     newAttributes[this.columnName] = {
       type: DataTypes.INTEGER,
-      allowNull: false
+      allowNull: false,
+      defaultValue: Utils._.partial(
+        Utils.toDefaultValue,
+        0
+      )
     };
 
-    // apparently you can't set defaultValues after model definition
-    this.source._defaultValues[this.columnName] = Utils._.partial(
-      Utils.toDefaultValue,
-      0
-    );
-    this.source._hasDefaultValues = true;
-
     Utils.mergeDefaults(this.source.rawAttributes, newAttributes);
 
     // Sync attributes and setters/getters to DAO prototype